This study investigated how people detect changes to visual shapes using a change detection task. Observers viewed two shapes sequentially and reported if they were the same or different. The study found that people were much better at detecting changes involving the addition or removal of a concavity (indentation) compared to equally sized changes involving convexities (outward curves). This suggests that the visual system represents concavities in shapes more explicitly than convexities. The findings provide insights into the underlying representation of visual shape and how change detection can be used to study visual representations.
Priprema koja (uopšteno) prikazuje jedan mogući model govorne vežbe, koja se može izvoditi samostalno, direktno vezana za gradivo, knj. tekst, ili pak kao priprema za pismenu vežbu.
Attention Makes Moving Objects Be Perceived To Move FasterAmy Roman
Attention can alter the perceived speed of moving objects. In five experiments, attended moving stimuli were judged to move faster than less attended stimuli. However, the change in perceived speed did not correspond to an actual change in the phenomenological appearance of the speed. While attention affects motion perception performance, it does not seem to directly alter the perceived speed of a moving object.
Cephalometrics history, evolution, and land marks/orthodontic courses by indi...Indian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
A Critical Boundary To The Left-Hemisphere Advantage In Visual-Word ProcessingGina Brown
1) Two experiments explored conditions where the typical left-hemisphere advantage in visual word recognition is reduced or eliminated.
2) The experiments found that the left-hemisphere advantage was weaker for words in alternating case and was numerically reversed for words in an unfamiliar prototype font.
3) These results are consistent with the theory that dissociable abstract and specific neural systems underlie visual word recognition in each hemisphere, rather than a single visual lexicon located in the left hemisphere.
Size Constancy and Accommodation, Maturana & Varela, 1981David Alcántara
This document discusses the role of accommodation in size constancy and perception of distance. It presents evidence that:
1) Accommodation operates in a perceptually effective manner for distances far beyond the usually assumed limit of a few meters.
2) The perceptual correlates of accommodation are involved in discriminating distances well beyond limits suggested by purely optical considerations.
3) The phenomenon of size constancy is best explained by its link to the neuronal activity involved in the effort of accommodation, not just the physical changes in lens curvature.
1) The study investigated how perceptual grouping of elements into objects influences the deployment of attention in multielement displays.
2) Using Bundesen's Theory of Visual Attention, the researchers assessed effects on top-down control of attention and the spatial distribution of attention weights.
3) In two experiments, participants reported letters from briefly presented displays where letter pairs could be connected. Results showed that grouping along the task-relevant dimension increased top-down control and the tendency to report within-object letter pairs, while task-irrelevant grouping did not affect performance.
Priprema koja (uopšteno) prikazuje jedan mogući model govorne vežbe, koja se može izvoditi samostalno, direktno vezana za gradivo, knj. tekst, ili pak kao priprema za pismenu vežbu.
Attention Makes Moving Objects Be Perceived To Move FasterAmy Roman
Attention can alter the perceived speed of moving objects. In five experiments, attended moving stimuli were judged to move faster than less attended stimuli. However, the change in perceived speed did not correspond to an actual change in the phenomenological appearance of the speed. While attention affects motion perception performance, it does not seem to directly alter the perceived speed of a moving object.
Cephalometrics history, evolution, and land marks/orthodontic courses by indi...Indian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
A Critical Boundary To The Left-Hemisphere Advantage In Visual-Word ProcessingGina Brown
1) Two experiments explored conditions where the typical left-hemisphere advantage in visual word recognition is reduced or eliminated.
2) The experiments found that the left-hemisphere advantage was weaker for words in alternating case and was numerically reversed for words in an unfamiliar prototype font.
3) These results are consistent with the theory that dissociable abstract and specific neural systems underlie visual word recognition in each hemisphere, rather than a single visual lexicon located in the left hemisphere.
Size Constancy and Accommodation, Maturana & Varela, 1981David Alcántara
This document discusses the role of accommodation in size constancy and perception of distance. It presents evidence that:
1) Accommodation operates in a perceptually effective manner for distances far beyond the usually assumed limit of a few meters.
2) The perceptual correlates of accommodation are involved in discriminating distances well beyond limits suggested by purely optical considerations.
3) The phenomenon of size constancy is best explained by its link to the neuronal activity involved in the effort of accommodation, not just the physical changes in lens curvature.
1) The study investigated how perceptual grouping of elements into objects influences the deployment of attention in multielement displays.
2) Using Bundesen's Theory of Visual Attention, the researchers assessed effects on top-down control of attention and the spatial distribution of attention weights.
3) In two experiments, participants reported letters from briefly presented displays where letter pairs could be connected. Results showed that grouping along the task-relevant dimension increased top-down control and the tendency to report within-object letter pairs, while task-irrelevant grouping did not affect performance.
This document presents a method for calculating asymptotic confidence intervals for indirect effects in structural equation models. The author first shows that under maximum likelihood estimation, the coefficient vector in a recursive structural equation model is asymptotically normally distributed. Then, using the multivariate delta method, it is shown that nonlinear functions of the coefficients, such as indirect effects, are also asymptotically normally distributed. This allows confidence intervals to be constructed for indirect effects based on their asymptotic distribution. An example is worked through to demonstrate the method.
Dimensionality Reduction Techniques In Response Surface Designsinventionjournals
Dimensionality reduction has enormous applications in various fields in industries. It can be applied in an optimal way with respect to time and cost related to the agricultural sciences, mechanical engineering, chemical technology, pharmaceutical sciences, clinical trials, biological studies, image processing, pattern recognitions etc. Several researchers made attempts on the reduction of the size of the model for different specific problems using some mathematical and statistical techniques identifying and eliminating some insignificant variables.This paper presents a review of the available literature on dimensionality reduction
Adaptationism And Molecular Biology An Example Based On ADHDFaith Brown
This document discusses issues with the adaptationist approach taken in evolutionary psychology research. It summarizes an alternative approach proposed by the authors that begins with identifying candidate genes associated with traits, then testing for patterns of selection at the DNA level before speculating about adaptations. As an example, the authors discuss research on the dopamine receptor D4 (DRD4) gene and its association with Attention Deficit Hyperactivity Disorder (ADHD). They found evidence that a specific allele of this gene (7R) may confer advantages in conflict resolution and is more prevalent in ADHD samples. The authors argue this molecular genetic approach can help limit the number of hypotheses about adaptations that need to be considered and avoid issues with relying solely on complex clinical literature.
Automatic eye fixations identification based on analysis of variance and cova...Giuseppe Fineschi
Eye movement is the simplest and repetitive movement that enables humans to interact with the environment. The common daily activities, such as reading a book or watching television, involve this natural
activity, which consists of rapidly shifting our gaze from one region to another. In clinical application, the
identification of the main components of eye movement during visual exploration, such as fixations and
saccades, is the objective of the analysis of eye movements: however, in patients affected by motor control disorder the identification of fixation is not banal. This work presents a new fixation identification
algorithm based on the analysis of variance and covariance: the main idea was to use bivariate statistical
analysis to compare variance overxandyto identify fixation. We describe the new algorithm, and we
compare it with the common fixations algorithm based on dispersion. To demonstrate the performance
of our approach, we tested the algorithm in a group of healthy subjects and patients affected by motor
control disorder
This document presents Anne Treisman and Garry Gelade's feature-integration theory of attention. The theory proposes that visual features are initially processed in parallel across the visual field, while objects are identified separately and require focused attention. A number of experiments are described that test predictions of the theory regarding visual search, texture segregation, illusory conjunctions, and the relationship between identification and localization of visual stimuli. The results provide general support for the theory and its distinction between the parallel processing of visual features and the serial processing required to integrate features into objects.
This document discusses challenges in conveying depth perception and physical orientation through technical illustrations. It reports that:
1) Readers best understood illustrations shown directly from the front or back, and least understood side views or those rotated partially from front/back.
2) On average, readers correctly matched body positions in illustrations only 45% of the time. Views involving distances into the display plane were hardest to judge accurately.
3) Ongoing analysis is examining the effects of varying heights, displacements, camera angles, and object types on performance in tasks depicted through illustrations. Future applications like free viewpoint video may revolutionize interactive manuals but also enable spatial misconceptions.
1. The document discusses gender differences in spatial orientation abilities and wayfinding strategies.
2. It analyzes results from experiments that assessed how well males and females could locate themselves on maps and find directions, finding that males performed better on some route and survey tasks.
3. Visuospatial working memory (VSWM) was found to better predict orientation abilities for males than females, and active processing tasks predicted performance better for females, suggesting they use different strategies.
Testing the dual-route model about the Simon effect with a replicated go-/no-go task, this experiment revealed that conditional trials did not exercise an inhibitory effect on subsequent response decisions.
This article reviews brain imaging studies that examine the hypothesis that perception and action share a common representational framework based on behavioral evidence. The authors discuss evidence from behavioral studies that suggest observers understand actions by applying the same neural representations they use to produce those actions. However, the authors argue that current neurophysiological evidence does not conclusively demonstrate a clear neural substrate that supports a common coding between perception and action. The article examines what is known about the functional organization of the visual system from primate and human studies and discusses models of the dorsal and ventral visual pathways and their different roles in perception and action.
This article reviews brain imaging studies that examine the hypothesis that perception and action share a common representational framework based on behavioral evidence. The authors discuss evidence from behavioral studies that suggest observers understand actions by applying the same neural representations they use to produce those actions. However, the authors argue that current neurophysiological evidence does not conclusively support a clear neural basis for this common coding between perception and action. The article examines what is known about the functional organization of the visual system into the ventral and dorsal pathways and discusses models of their different roles in recognition versus action guidance.
1. The document discusses neural mechanisms underlying the perception of human actions. It reviews brain imaging studies that have examined areas activated during the observation of human movement.
2. A key area found to be activated across studies is V5, which is involved in visual motion processing. Other areas activated include the superior temporal gyrus and ventral and dorsal areas of V3.
3. The studies provide some evidence for the involvement of both the dorsal and ventral visual pathways during action perception, though the specific contributions of each pathway require further investigation.
Is there a difference in the pattern of eye movements during visual imagery w...James Allen
This study investigated differences in eye movement patterns during visual imagery of spatial versus object information. 20 subjects viewed arrays of 4 shapes and were asked to recall either the location ("where") or attribute ("what") of a shape. Eye movements were recorded during recall and when simply imagining shapes. Recall of spatial information elicited significantly longer fixations and more fixations in the correct location compared to recall of object information. Subjects' visual working memory did not interact with eye movements. The results provide evidence that visual imagery of spatial and object information interacts differently with eye movements and the brain processes these types of information differently.
Marginal Regression for a Bi-variate Response with Diabetes Mellitus Studytheijes
In this paper, we have developed an “A Bivariate response” model to determine for „A Diabetic Mellitus‟ Study affects large number of people of all social conditions throughout the world. Continuous to grow despite of existing advances in the past few years in virtually every fled of diabetes research and in-protect care for improved treatment. This is sometimes accompanied by symptoms of serve thirst. Profuse urination, weight loss and stopper. We tested by SPSS software by taking 200 samples and using Logistic Regression to estimate the relationship between the response probability whether a diabetic patient had B.P. or not.
This document summarizes research on spontaneous body movements during spatial tasks. The researchers measured small head rotations performed by participants during a perspective-taking task inspired by map reading. They found these head rotations were significantly related to the task and seemed to represent participants trying to align themselves with orientations on the map, though in very small amplitudes. This supports the idea that spatial reasoning involves a sensorimotor prediction mechanism triggered by planned movements, even if the movements themselves are inhibited and only traces are observed.
This study compared two methods for sexing skulls - Method 1 used descriptions only while Method 2 used illustrations and descriptions. Two observers sexed 50 skulls of unknown sex twice using each method. There was no significant difference in average intraobserver agreement between the two methods. However, interobserver agreement was higher for most traits in Method 1 compared to Method 2. The results indicate that while the methods have similar reliability, Method 1 may be less subjective. Overall, subjectivity remained high for both methods.
Change Blindness With Scene Themes And Adding And Deleting ObjectsGinaMMartino
People often times fail to detect changes in scenes they observe. We examined theme, whether an object was related to a scene or not, as well as object change, whether the object was added or deleted to the previous scene, would effect the reaction time in identifying a change. Participants were randomly assigned to one of two object change conditions (add or delete) and then were asked to judge whether or not there was a change involving scenes with related objects changing, as well as scenes with unrelated objects changing. The results showed a main effect of theme but no main effect of object change as well as no interaction between the two independent variables.
An international group of clinicians established a process to standardize terminology used to describe human morphology. They define general terms commonly used for congenital anomalies. The definitions aim to increase precision in phenotypic descriptions and facilitate comparisons among researchers. Key terms defined include anomaly, variant, syndrome and their subtypes. The goals are to clarify usage and account for advances in genetics and developmental biology.
This systematic review analyzed 12 controlled trials that compared the effects of different insoles on postural balance. The insoles studied included vibrating insoles, textured insoles, insoles with different densities, and insoles with wedges or sensors. Most studies found that the insoles improved postural balance and reduced sway, especially in the anteroposterior direction. Textured insoles and vibrating insoles showed benefits by increasing sensory input from the feet. While insole rigidity did not influence balance, soft gel insoles and insoles with spikes were found to improve postural control. The review concluded that insoles can provide benefits that favor better postural balance and control.
This document summarizes a study examining the relationship between fluid intelligence and deficits on executive function tests after frontal lobe lesions. The study assessed whether deficits on executive function tests could be fully explained by reduced fluid intelligence, or if some tests showed additional deficits related to specific impaired regions. The study found that for some widely used tests like the Wisconsin Card Sorting Test, fluid intelligence entirely explained performance deficits after frontal lobe lesions. However, for other tests of cognitive and social functions, deficits were only partially explained by fluid intelligence and seemed to associate with lesions in the right anterior frontal cortex. Understanding the relationships between fluid intelligence deficits, more specific impairments, and their brain regions can help clarify the nature of frontal lobe deficits.
This document provides an overview and guidelines for developing different chapters of a research paper, including the introduction, literature review, and methodology sections.
The introduction chapter should include a rationale explaining the need for the study and a problem statement clearly outlining the research problem or question. It also defines any important terms and states the purpose and significance of the study.
The literature review chapter summarizes and critiques previous research relevant to the topic. It is organized by topic and presents related literature and studies in a logical order.
The methodology chapter describes the research methods and procedures used in the study, including the research design, environment/location of the study, population and sampling techniques, data collection instruments and procedures, and methods
This document presents a method for calculating asymptotic confidence intervals for indirect effects in structural equation models. The author first shows that under maximum likelihood estimation, the coefficient vector in a recursive structural equation model is asymptotically normally distributed. Then, using the multivariate delta method, it is shown that nonlinear functions of the coefficients, such as indirect effects, are also asymptotically normally distributed. This allows confidence intervals to be constructed for indirect effects based on their asymptotic distribution. An example is worked through to demonstrate the method.
Dimensionality Reduction Techniques In Response Surface Designsinventionjournals
Dimensionality reduction has enormous applications in various fields in industries. It can be applied in an optimal way with respect to time and cost related to the agricultural sciences, mechanical engineering, chemical technology, pharmaceutical sciences, clinical trials, biological studies, image processing, pattern recognitions etc. Several researchers made attempts on the reduction of the size of the model for different specific problems using some mathematical and statistical techniques identifying and eliminating some insignificant variables.This paper presents a review of the available literature on dimensionality reduction
Adaptationism And Molecular Biology An Example Based On ADHDFaith Brown
This document discusses issues with the adaptationist approach taken in evolutionary psychology research. It summarizes an alternative approach proposed by the authors that begins with identifying candidate genes associated with traits, then testing for patterns of selection at the DNA level before speculating about adaptations. As an example, the authors discuss research on the dopamine receptor D4 (DRD4) gene and its association with Attention Deficit Hyperactivity Disorder (ADHD). They found evidence that a specific allele of this gene (7R) may confer advantages in conflict resolution and is more prevalent in ADHD samples. The authors argue this molecular genetic approach can help limit the number of hypotheses about adaptations that need to be considered and avoid issues with relying solely on complex clinical literature.
Automatic eye fixations identification based on analysis of variance and cova...Giuseppe Fineschi
Eye movement is the simplest and repetitive movement that enables humans to interact with the environment. The common daily activities, such as reading a book or watching television, involve this natural
activity, which consists of rapidly shifting our gaze from one region to another. In clinical application, the
identification of the main components of eye movement during visual exploration, such as fixations and
saccades, is the objective of the analysis of eye movements: however, in patients affected by motor control disorder the identification of fixation is not banal. This work presents a new fixation identification
algorithm based on the analysis of variance and covariance: the main idea was to use bivariate statistical
analysis to compare variance overxandyto identify fixation. We describe the new algorithm, and we
compare it with the common fixations algorithm based on dispersion. To demonstrate the performance
of our approach, we tested the algorithm in a group of healthy subjects and patients affected by motor
control disorder
This document presents Anne Treisman and Garry Gelade's feature-integration theory of attention. The theory proposes that visual features are initially processed in parallel across the visual field, while objects are identified separately and require focused attention. A number of experiments are described that test predictions of the theory regarding visual search, texture segregation, illusory conjunctions, and the relationship between identification and localization of visual stimuli. The results provide general support for the theory and its distinction between the parallel processing of visual features and the serial processing required to integrate features into objects.
This document discusses challenges in conveying depth perception and physical orientation through technical illustrations. It reports that:
1) Readers best understood illustrations shown directly from the front or back, and least understood side views or those rotated partially from front/back.
2) On average, readers correctly matched body positions in illustrations only 45% of the time. Views involving distances into the display plane were hardest to judge accurately.
3) Ongoing analysis is examining the effects of varying heights, displacements, camera angles, and object types on performance in tasks depicted through illustrations. Future applications like free viewpoint video may revolutionize interactive manuals but also enable spatial misconceptions.
1. The document discusses gender differences in spatial orientation abilities and wayfinding strategies.
2. It analyzes results from experiments that assessed how well males and females could locate themselves on maps and find directions, finding that males performed better on some route and survey tasks.
3. Visuospatial working memory (VSWM) was found to better predict orientation abilities for males than females, and active processing tasks predicted performance better for females, suggesting they use different strategies.
Testing the dual-route model about the Simon effect with a replicated go-/no-go task, this experiment revealed that conditional trials did not exercise an inhibitory effect on subsequent response decisions.
This article reviews brain imaging studies that examine the hypothesis that perception and action share a common representational framework based on behavioral evidence. The authors discuss evidence from behavioral studies that suggest observers understand actions by applying the same neural representations they use to produce those actions. However, the authors argue that current neurophysiological evidence does not conclusively demonstrate a clear neural substrate that supports a common coding between perception and action. The article examines what is known about the functional organization of the visual system from primate and human studies and discusses models of the dorsal and ventral visual pathways and their different roles in perception and action.
This article reviews brain imaging studies that examine the hypothesis that perception and action share a common representational framework based on behavioral evidence. The authors discuss evidence from behavioral studies that suggest observers understand actions by applying the same neural representations they use to produce those actions. However, the authors argue that current neurophysiological evidence does not conclusively support a clear neural basis for this common coding between perception and action. The article examines what is known about the functional organization of the visual system into the ventral and dorsal pathways and discusses models of their different roles in recognition versus action guidance.
1. The document discusses neural mechanisms underlying the perception of human actions. It reviews brain imaging studies that have examined areas activated during the observation of human movement.
2. A key area found to be activated across studies is V5, which is involved in visual motion processing. Other areas activated include the superior temporal gyrus and ventral and dorsal areas of V3.
3. The studies provide some evidence for the involvement of both the dorsal and ventral visual pathways during action perception, though the specific contributions of each pathway require further investigation.
Is there a difference in the pattern of eye movements during visual imagery w...James Allen
This study investigated differences in eye movement patterns during visual imagery of spatial versus object information. 20 subjects viewed arrays of 4 shapes and were asked to recall either the location ("where") or attribute ("what") of a shape. Eye movements were recorded during recall and when simply imagining shapes. Recall of spatial information elicited significantly longer fixations and more fixations in the correct location compared to recall of object information. Subjects' visual working memory did not interact with eye movements. The results provide evidence that visual imagery of spatial and object information interacts differently with eye movements and the brain processes these types of information differently.
Marginal Regression for a Bi-variate Response with Diabetes Mellitus Studytheijes
In this paper, we have developed an “A Bivariate response” model to determine for „A Diabetic Mellitus‟ Study affects large number of people of all social conditions throughout the world. Continuous to grow despite of existing advances in the past few years in virtually every fled of diabetes research and in-protect care for improved treatment. This is sometimes accompanied by symptoms of serve thirst. Profuse urination, weight loss and stopper. We tested by SPSS software by taking 200 samples and using Logistic Regression to estimate the relationship between the response probability whether a diabetic patient had B.P. or not.
This document summarizes research on spontaneous body movements during spatial tasks. The researchers measured small head rotations performed by participants during a perspective-taking task inspired by map reading. They found these head rotations were significantly related to the task and seemed to represent participants trying to align themselves with orientations on the map, though in very small amplitudes. This supports the idea that spatial reasoning involves a sensorimotor prediction mechanism triggered by planned movements, even if the movements themselves are inhibited and only traces are observed.
This study compared two methods for sexing skulls - Method 1 used descriptions only while Method 2 used illustrations and descriptions. Two observers sexed 50 skulls of unknown sex twice using each method. There was no significant difference in average intraobserver agreement between the two methods. However, interobserver agreement was higher for most traits in Method 1 compared to Method 2. The results indicate that while the methods have similar reliability, Method 1 may be less subjective. Overall, subjectivity remained high for both methods.
Change Blindness With Scene Themes And Adding And Deleting ObjectsGinaMMartino
People often times fail to detect changes in scenes they observe. We examined theme, whether an object was related to a scene or not, as well as object change, whether the object was added or deleted to the previous scene, would effect the reaction time in identifying a change. Participants were randomly assigned to one of two object change conditions (add or delete) and then were asked to judge whether or not there was a change involving scenes with related objects changing, as well as scenes with unrelated objects changing. The results showed a main effect of theme but no main effect of object change as well as no interaction between the two independent variables.
An international group of clinicians established a process to standardize terminology used to describe human morphology. They define general terms commonly used for congenital anomalies. The definitions aim to increase precision in phenotypic descriptions and facilitate comparisons among researchers. Key terms defined include anomaly, variant, syndrome and their subtypes. The goals are to clarify usage and account for advances in genetics and developmental biology.
This systematic review analyzed 12 controlled trials that compared the effects of different insoles on postural balance. The insoles studied included vibrating insoles, textured insoles, insoles with different densities, and insoles with wedges or sensors. Most studies found that the insoles improved postural balance and reduced sway, especially in the anteroposterior direction. Textured insoles and vibrating insoles showed benefits by increasing sensory input from the feet. While insole rigidity did not influence balance, soft gel insoles and insoles with spikes were found to improve postural control. The review concluded that insoles can provide benefits that favor better postural balance and control.
This document summarizes a study examining the relationship between fluid intelligence and deficits on executive function tests after frontal lobe lesions. The study assessed whether deficits on executive function tests could be fully explained by reduced fluid intelligence, or if some tests showed additional deficits related to specific impaired regions. The study found that for some widely used tests like the Wisconsin Card Sorting Test, fluid intelligence entirely explained performance deficits after frontal lobe lesions. However, for other tests of cognitive and social functions, deficits were only partially explained by fluid intelligence and seemed to associate with lesions in the right anterior frontal cortex. Understanding the relationships between fluid intelligence deficits, more specific impairments, and their brain regions can help clarify the nature of frontal lobe deficits.
This document provides an overview and guidelines for developing different chapters of a research paper, including the introduction, literature review, and methodology sections.
The introduction chapter should include a rationale explaining the need for the study and a problem statement clearly outlining the research problem or question. It also defines any important terms and states the purpose and significance of the study.
The literature review chapter summarizes and critiques previous research relevant to the topic. It is organized by topic and presents related literature and studies in a logical order.
The methodology chapter describes the research methods and procedures used in the study, including the research design, environment/location of the study, population and sampling techniques, data collection instruments and procedures, and methods
1. Cognition 89 (2003) 1–9
www.elsevier.com/locate/COGNIT
Detection of change in shape:
an advantage for concavities
Elan Barenholtz*, Elias H. Cohen, Jacob Feldman, Manish Singh
Department of Psychology, Center for Cognitive Science, Rutgers University – New Brunswick, Busch Campus,
152 Frelinghuysen Road, Piscataway, NJ 08854-8020, USA
Received 5 November 2002; accepted 23 January 2003
Abstract
Shape representation was studied using a change detection task. Observers viewed two individual
shapes in succession, either identical or one a slightly altered version of the other, and reported
whether they detected a change. We found a dramatic advantage for concave compared to convex
changes of equal magnitude. Observers were more accurate when a concavity along the contour was
introduced, or removed, compared to a convexity. This result sheds light on the underlying
representation of visual shape, and in particular the central role played by part-boundaries.
Moreover, this finding shows how change detection methodology can serve as a useful tool in
studying the specific form of visual representations.
q 2003 Elsevier Science B.V. All rights reserved.
Keywords: Change detection; Shape; Part-boundaries; Convexity; Concavity
1. Introduction
The representation of shape remains one of the most difficult puzzles in visual
cognition. One obstacle to progress has been a lack of good experimental methods for
evaluating shape representations. In this paper, we introduce a method for analyzing visual
shape representation that is based on a change detection task. In our task, observers view
two sequentially presented shapes that are either identical or slightly different and attempt
to determine whether they are the same or not, or in other words, to determine whether
there has been a change to the stimulus. While change detection is of course not new, past
* Corresponding author.
E-mail addresses: elanbz@ruccs.rutgers.edu (E. Barenholtz), elias@ruccs.rutgers.edu (E.H. Cohen),
jacob@ruccs.rutgers.edu (J. Feldman), manish@ruccs.rutgers.edu (M. Singh).
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0010-0277(03)00068-4
2. 2 E. Barenholtz et al. / Cognition 89 (2003) 1–9
studies have focused largely on the architectural limitations – such as constraints of
memory, attention, etc. – that influence detectability of change in complex displays. By
contrast, in our study we are interested in comparing sensitivities to different types
of changes taking place along the contour of a single, simple shape. In the spirit of
Marr (1982), we assume that visual representations make explicit particular aspects of the
structure of the scene while discarding others or leaving them implicit. Thus, we predict
that observers will be preferentially sensitive to changes in those aspects that the visual
system represents explicitly, and relatively insensitive to those that it does not. By this
argument, detectability differences among types of shape change would shed light on the
underlying representation of shape.
A number of important elements of shape representation have been identified. The
magnitude of curvature along a contour has long been understood to be an important
psychological dimension (Attneave, 1954), with an especially significant role played by
curvature extrema (points where curvature, or the degree of “bending”, is locally
maximal). More recently the distinction between concave and convex bending (called
negative and positive curvature, respectively) has been found to be psychologically
important, with maximally concave extrema (technically called negative minima of
curvature) serving as candidate part-boundaries (Hoffman & Richards, 1984; Koenderink,
1984; see also Barenholtz & Feldman, in press; Hoffman & Singh, 1997). These findings
mirror regularities in the visual world, where concave contour segments often correspond
to loci where one part of an object ends and another begins: for example, at the intersection
of a tabletop with one of its legs.
Can the representational asymmetry between convexity and concavity be manifested in
change detection? If it is indeed the case that concavities have a special status in the
representation of visual shape, then we might expect that human observers will be more
sensitive to changes that occur along concave segments of a shape than changes that occur
along convex segments. Our experiment aims to test this hypothesis by presenting
observers with convex and concave changes that are of equal magnitude. A differential
sensitivity to one type of change over the other will thus point to a difference in the
underlying representation.
The change detection methodology was first introduced by Phillips and Singer
(Phillips, 1974; Phillips & Singer, 1973) to investigate the difference between low-level
transient detection and visual short-term memory. In those studies, observers were shown
two displays in succession with a variable inter-stimulus interval, and asked to indicate
whether a change had taken place. More recently this paradigm has received a great deal of
attention because of the finding that even gross changes in the scene (e.g. the addition or
subtraction of an entire background object) can be extremely difficult to detect (sometimes
called “change blindness”; Rensink, O’Regan, & Clark, 1997; Simons & Levin, 1997),
especially if their location was not previously attended (Scholl, 2000), or foveated
(Henderson & Hollingworth, 1999). These findings have caused some controversy, in part
because they have sometimes been accompanied by strong claims about the degree to
which the visual system maintains any representation of the scene (see for example
Ballard, Hayhoe, Pook, & Rao, 1997). Our aim in the current study was not to engage these
larger issues concerning the extent of processing and the limits of mental representation,
but rather to use similar methodology to assess the actual content of representations. As
3. E. Barenholtz et al. / Cognition 89 (2003) 1–9 3
Fig. 1. (a) Polygon pairs used in the experiment consisted of a ‘Base’ shape and a modified version of this shape
with either an additional concavity or convexity. (b) The four (2 £ 2) types of changes that appeared in the
experiment with the arrow directions signifying sequence order: in the “Introduce” case the base shape was
presented first, followed by the modified shape, while in the “Remove” case this order was reversed.
discussed above, the presence of ‘change blindness’ has generally been found to occur
within complex displays containing multiple objects. The observed deficits in these studies
are generally described as a failure to process unattended regions or objects within the
display. By contrast, our study, using displays that are limited to a single attended shape, is
concerned not with the overall efficiency of change detection but rather with comparative
sensitivities to different types of changes. If observers are systematically more sensitive to
changes affecting one dimension of shape as compared to another – regardless of where
within the shape they take place – we may infer that that dimension is more explicitly
represented in the visual system. Differential sensitivity implies differential representation.
4. 4 E. Barenholtz et al. / Cognition 89 (2003) 1–9
2. Experiment
Each of our stimuli consisted of a single unfamiliar “nonsense” polygon, generated
randomly under certain constraints (see methods below). An alternate version of this basic
shape was created by either adding (introducing) or subtracting (removing) a single vertex
from the base shape, in such a way that the new vertex either lay inside or outside the
original shape yielding, respectively, either a concave indentation or a convex
protrusion (see Fig. 1). This yielded a 2 £ 2 factorial design of change direction
(introduce or remove) by change type (concave or convex). (For examples of the
displays, see http://ruccs.rutgers.edu/~elanbz/changedemos.htm.) On change trials (50%
of trials), these two shapes were then shown in succession, with a brief mask intervening;
on no-change trials, shapes shown on successive screens were identical. The observer’s
forced-choice task was to indicate “change” or “no-change”. In contrast to most studies in
the change detection literature, we report observers’ performance in terms of absolute
sensitivity (d0 ), so that we may distinguish between true differences in sensitivity and shifts
in the criterion for responding “change”. This also allows us to clearly identify conditions
of absolute “change blindness” (d 0 ¼ 0).
2.1. Method
2.1.1. Observers
Eleven Rutgers undergraduates served as naive observers for course credit.
2.1.2. Stimuli
Stimuli were computer-generated filled polygons (of randomly assigned color)
measuring approximately 2.4– 4.8 degrees in both height and width. The polygons were
generated as triads consisting of a “base” shape and two “changed” versions of that shape:
one with an additional concavity and one with an additional convexity (see Fig. 1a). The
base shape was generated by choosing between nine and 12 points, each lying at a random
location along successive (clockwise) radial axes, projecting from the center of the screen,
and joined by line segments. As each successive point was chosen it was checked to
determine whether it resulted in a convex or concave vertex; if the vertex resulted in a
concavity, it was discarded and a new point was chosen. Once this convex shape was
complete, between zero and two concavities were added (procedure described below). An
equal number of zero-, one-, and two-concavity shapes were included in the set of base
shapes.
The two “changed” versions were each generated by modifying the base shape in one of
two ways: by introducing an additional concavity or by introducing an additional
convexity. The procedure for introducing both concavities and convexities was to
randomly choose an edge of the base shape, translate its midpoint perpendicularly to the
edge (towards the center for the concave version, and away for the convex version), and
join this new vertex to its neighboring points with two new line segments (see Fig. 1b).
The size of the concavity/convexity (measured as the distance of translation of the point)
was randomly varied between five and 30 pixels on each trial. Translations of the changed
5. E. Barenholtz et al. / Cognition 89 (2003) 1–9 5
Fig. 2. Schematic diagram of the experimental sequence: (A) fixation point; (B) first shape stimulus; (C) mask;
(D) second shape stimulus; (E) mask.
vertices measured between 0.06 and 0.37 degrees from the original edge. A new set of
polygons was generated for each observer.
2.1.3. Procedure
The task was two-way, forced choice. On each trial, the observer was presented with the
following sequence (Fig. 2): (1) a fixation cross presented for a variable duration between
300 and 700 ms; (2) the first shape stimulus for 250 ms; (3) a mask for 200 ms; (4) the
second shape stimulus for 250 ms; and (5) the mask until response. There were two
independent variables in the Change trials: Change Type (Concave/Convex), and Change
Direction (Introduce/Remove). On the “No-Change” trials (half), the base shape was
simply displayed twice. In the change trials, there were four possible types of “Change”
(see Fig. 1b). In the “Introduce” cases, the base shape was shown first, followed by the
“changed” shape (either concave or convex); this order was reversed for the “Remove”
cases. The observer responded using the keypad, with feedback provided by a beep on
incorrect responses.
2.1.4. Design
Each experimental block contained 96 trials (48 change, 48 no-change). This quantity
allowed for the crossing of the two experimental variables (2 £ 2) for change trials as well
as balancing for both number of concavities and sides in the base shape for both change
and no-change trials. Each observer ran eight blocks for a total of 768 trials.
6. 6 E. Barenholtz et al. / Cognition 89 (2003) 1–9
Fig. 3. Mean performance (d0 ) as a function of change type (convex vs. concave) and change direction
(introduction vs. removal).
Fig. 4. Mean performance as a function of the magnitude of change. The x-axis corresponds to the average
distance, in degrees visual angle, towards (concave changes) or away from (convex changes) the interior of the
shape.
7. E. Barenholtz et al. / Cognition 89 (2003) 1–9 7
3. Results
Accuracy was much better for concave (mean ¼ 70:83%, SE ¼ 4:0%) than convex
(mean ¼ 36:94%, SE ¼ 4:0%) changes. Fig. 3 shows mean performance converted to d0 as
a function of change type (convex vs. concave) and change direction (introduction vs.
removal). d0 performance (convex mean ¼ 0:2960, SE ¼ 0:089; concave mean ¼ 1:2815,
SE ¼ 0:229) was subjected to an analysis of variance. The difference between concave
and convex change was highly significant (Fð1; 10Þ ¼ 40:34, P , 0:0001). There was no
significant effect of change direction (introduction vs. removal), and no significant
interaction (P . 0:25 in both cases).
Fig. 4 shows accuracy as a function of the magnitude of change (i.e. the distance from
the base shape to the new vertex in the changed shape). As one would expect, observers’
ability to detect changes increased with magnitude. However, a substantial advantage for
concave changes is evident at all magnitudes. This is especially important because
concave changes are generally towards the center of the shape (and thus closer to fixation),
which might be expected to lead to a detectability advantage. But as is clear from Fig. 4,
even at small magnitudes – where the difference in eccentricity is negligible – there is still
a large detectability advantage for concave over convex changes, demonstrating that the
concavity effect cannot be attributed to eccentricity differences alone.
4. Discussion
These results provide strong evidence for the differential representation of concavities
and convexities by the visual system. The advantage for detecting concavities compared to
convexities was found whether the concavity/convexity was introduced or removed, and
was stable across all the levels of magnitude – including the smallest levels, where
subjects were essentially “blind” (d0 ¼ 0) to convex, but not concave, changes. The
current findings are consistent with results in the domain of visual search (Hullman, te
Winkel, & Boselie, 2000; Wolfe & Bennett, 1997) in which concavities have been found
to behave as “basic features” (shapes with concavities “pop out” in a field of convex
shapes but not vice-versa). Our results similarly point to the importance of concavities in
visual shape representation.
There are at least two types of hypotheses that might account for the asymmetry
between concavities and convexities, which can be termed “localist” and “globalist”. The
localist hypothesis is that concave sections of contour are inherently more salient,
irrespective of the eventual role they play in shape decomposition. High-curvature
segments of a curve literally carry more information than low-curvature sections
(Attneave, 1954; Resnikoff, 1985), and concave segments more than convex ones
(Feldman & Singh, 2003). The differential sensitivity observed here might stem directly
from this informational asymmetry. Alternatively, given that global organization
sometimes takes precedence (Palmer, 1977; Pomerantz, Sager, & Stoever, 1977), another
possibility is that concave regions are especially detectable because – and only insofar as
– they influence the global decomposition of the shape into parts. Introducing or removing
a concavity often changes the number of perceived parts – a part either splits into two, or
8. 8 E. Barenholtz et al. / Cognition 89 (2003) 1–9
two parts coalesce into one – whereas introducing or removing a convexity leaves the
number of perceived parts unchanged, influencing only the shape of an existing part. It
may be that observers are only sensitive to changes in this overall organization per se
(Bertamini, 2001; Keane, Hayward, & Burke, 2003), and not to changes in local contour
regions. One intriguing variant of this account is that subjects might be preattentively
determining the number of parts in the shape – i.e. subitizing them (cf. Trick & Pylyshyn,
1994; van Oeffelen & Vos, 1982) – and are especially sensitive to changes in this number.
In any case, many questions remain to be resolved regarding the mechanisms by which
contour structure influences the global part interpretation (see Siddiqi & Kimia, 1995;
Siddiqi, Tresness, & Kimia, 1996; Singh & Hoffman, 2001; Singh, Seyranian, & Hoffman,
1999). Distinguishing between the localist and globalist accounts of our result is a piece in
the larger puzzle of shape representation.
5. Conclusion
In a change detection task, observers exhibited far greater sensitivity to changes
affecting concavities than changes affecting convexities. This large sensitivity difference
suggests that concave and convex sections of a contour have extremely different
perceptual representations, notwithstanding their very similar geometries. These results
are also of great methodological interest: the change detection task employed here
provides a potentially powerful tool for isolating representational differences, which may
be readily extended to study many other aspects of visual representation.
Acknowledgements
We are grateful to two anonymous reviewers for comments on the manuscript. This
research was supported by NIH T32-MH19975-03 to E.B., NIH T32-MK19975-04 to
E.C., NSF SBR-9875175 to J.F., and NSF BCS-0216944 to M.S.
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