Problem : the world is at some remove. How do we achieve action at a distance ? We behave effectively with respect to the world. What makes that possible? What are the mechanisms that allow perceptual agents to achieve action at a distance?
Phenomena What kinds of properties of the world are perceived? Philosophy What kinds of properties and theoretical assumptions should anchor our theory of perception? Physics What kinds of properties are present or “recorded” in the energy media of the world? Physiology What kinds of properties can sense organs and nerve cells “record” and how doe these sense organs influence the perception? What do we have to understand to understand the mechanisms of perception?
Phenomena What kinds of properties are perceived? Problem : the world is at some remove. How do we achieve action at a distance ? Themes from the Overview We behave effectively with respect to the world. What makes that possible? Philosophy What kinds of properties/assumptions should anchor our theory? Physics What kinds of properties are present or “recorded” in the energy media? Physiology What kinds of properties can sense organs and nerve cells “record”?
Indirect Realism We know the world through intermediaries eye is a chamber that captures images
… persist in modern view
copies stand between us and the world
eye as camera
disconnected sensations get connected higher up
light rays hit eye as pointillistic mosaic
The image is ambiguous, impoverished. (1) It doesn’t match the world. (2) It doesn’t match our experience. E nvironment O rganism link is bad therefore… Perception requires processes to elaborate input, constructing a series of representations of the world that increasingly come to resemble it. Examine the E O link How good are the images? Molyneux’s Premise (1692): distance is not perceivable by eye A B C D A B C D
What gets linked? What do you need to fix the bad link? Experience Knowledge: Empiricism 3 Old Guys who set the conceptual agenda An object in the world at some distance from me that goads me or stimulates me to act: distal stimulus or S D The pattern at a sense organ caused by an energy pattern in the world: proximal stimulus or S P
1. Berkeley (1700s) Eventually, visual image memories of motions idea of distance.
touch is the rationalizer
direct contact with the world
not susceptible to the loss of structure
can help out those senses that are susceptible
muscular feelings can help fix defects in visual image once I learn which images co-occur with which feelings .
extended arm grasps bottle contract arm— image expands 45˚ 90˚
worries about physiology & its psychological counterpart 2. Müller (1826)
Are stimulated by energy (light, sound, pressure)
But not mere conductors of those properties
Emphasizes the contribution of anatomy & physiology
Müller’s Theory of Specific Nerve Energies impose their own characteristics— “specific nerve energies”—on the mind. This, not the physical properties themselves, is why the qualities for the different senses are different. ELECTRIC PULSE PRESSURE CHEMICALS Visual sensation OPTIC NERVE LIGHT Eye designed to capture light SOUND AUDITORY NERVES Auditory sensation Ear designed to capture sound
3. Helmholtz (1821-1894): THE MAJOR FIGURE S D S P patchwork of sensations Helmholtz’s Theory of Unconscious Inference S P is converted to sensations —a mental response to energy ( direct ) Sensations that habitually occur together become linked through memory— associations . object
Normalcy is embodied in internal algorithms or rules. cues + rules = Unconscious Inference The input is a disjointed, inadequate copy of the world. Perception works by improving the copy via rules. Perception of the world is indirect .
The Perceptual Process: Attended Stimulus Environmental Stimulus Action Stimulus on the receptors Transduction Processing Perception Recognition Stimulus Perception Stimulus Energy Sensation Physiological sensation Perception Three key relationships Knowledge cues & rules Unconscious Inference
Berkeley: coupling of percepts uses meaningfulness of one to explain another Müller: the sensory apparatus itself contributes its character to the input Helmholtz: mental computations reflect internalized knowledge of the world and how it affects us. The nature of E S influences the nature of S P All share the theory of inadequate input currency is converted into currency: How does physical energy map onto psychological experience? Measurement is the key to making perceptual psychology a science World Energy Sensations Perception ignored link historically important links
The nature of E S influences the nature of S P currency is converted into currency: How does physical energy map onto psychological experience? Measurement is the key to making perceptual psychology a science World Energy Sensations Perception ignored link historically important links
Energy Sensation Experience Energy Sensation E S Physical Psychological Perceive event ( cat rubbing leg ) Event in world Pressure ( energy ) Sense properties of pressure ( ) e.g. amount, location. Pressure sensitive nerves Energy Sensation Psychophysics
Anticipated by Weber (mid-late 1800s) If the amount of energy is too small, it’s not noticeable. Psychophysics looks at the E S link minimum energy that can just be detected Say “now” when you see the gray square. Absolute threshold
Trial 1 Trial 2 No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes No Intensity (I) Determining the Absolute threshold: Method of Limits Trial 5 No No No No Yes Trial 3 No No No No No Yes Trial 4 No Yes Yes Yes Trial 6 Yes Yes Yes Yes Yes Yes No 3 4 5 6 7 8 9 10 2 1 11 12 0 6 5 4 1 3 2 Trial Smallest Intensity Detected 6 5 7 6 7 5 Absolute threshold Mean 6 6
Anticipated by Weber (mid-late 1800s) If change in amount of energy is too small, it’s not noticeable. Psychophysics looks at the E S link Weber’s focus was on discriminating two detectable stimuli: How similar could they be and still be sensed as different? Not absolute change but relative change J ust N oticeable D ifference I / I = K A change in intensity relative to the initial intensity equals a constant. – =
J ust N oticeable D ifference (JND) I sensed is not absolute!! Rather, the JND is a constant threshold. Difference Thresholds: How similar can objects be and still be sensed as different? I2 I1 102 g 100 g I2 - I1 = I I : physical intensity I2 I1 101 g 100 g Same
Consider what happens when we use different values of intensity (I) 100 + 2 = 102 2/100 = 1/50 (.02) 200 + 4 = 204 4/200 = 1/50 (.02) 400 + 8 = 408 8/400 = 1/50 (.02) The greater the value of I the greater must be the value of I for a difference to be sensed. JND’s for all senses: - Vision (e.g. change in brightness) - Hearing (e.g. change in loudness) WEBER’S LAW: = K (a constant) I I Intensity I JND I + I I I Change in I I K
I = 20 The correspondence between a physical stimulus and our perception of it is systematic but it is not always 1:1. I = 500 I = 500 smaller K more sensitive lower threshold K = 1 I = 20 I = 1000 I = 500 K = .5 I = 20 I = 10 I / I = K 1st truly quantitative law of psychology Fechner (mid-late 1800s) I I I I .2 .5 1 Slope
Weber’s goal was to study jnd s ; Fechner’s insight was that such a quantification allows you to probe mental states . Fechner (mid-late 1800s) Demonstrated how mental activity could be measured quantitatively!! … also started to examine whether we can assume a equivalence of changes in intensity of stimulation? Steven’s attempted to understand the relationships between and intensity in his examination of Magnitude estimation.
Subjective intensity of magnitide ( ) is some constant multiplied by the intensity (I) to some power (n). Stimulus Intensity Magnitude Estimate n = the slope of the line in the log-log plot Perceptual Sense reflects Power Law Functions Log Stimulus Intensity Log Magnitude Estimate = kI n
Implicit Metatheory: To say there is a absolute or noticeable threshold is to say that there are un-noticeable things. To say there is a just noticeable difference is to say that there are also un-noticeable differences. To say the perception is power law like is to say that the… Connection between mind & body is in the quantitative relation between mental sensation & material stimulus I/I = k and = kI n highlight slippage between & (not 1:1). How do you measure the change in stimulation? You need methods… … that yield quantities that can be put into law form Fechner formally developed Psychophysics as the methodology, a methodology that endorses a metatheory
Assumes the some currency has some currency May not be 1:1, but we must therefore understand: Understanding these things might help in understanding the processes of perception. Lets start with vision… Psychophysics looks at the E S link
The physics of different energy medium,
How the physiology is designed to transduce this energy and…
3. How his transduction maps onto sensory and psychological experience?
Understanding these things might help in understanding the processes of perception. Lets start with vision…
The physics of different energy medium,
How the physiology is designed to transduce this energy and…
3. How this transduction maps onto sensory and psychological experience?
currency is converted into currency: How does physical energy map onto psychological experience? World Energy Sensations Perception Assumes the some currency has some currency May not be 1:1, but we must therefore understand: Psychophysics looks at the E S link
Light: The stimulus for vision Electromagnetic radiation structured in waves * over space distance energy amplitude = Intensity Wavelength same amplitude different wavelengths multiple wavelengths (vs. pure) same wavelength different amplitude
Wavelength: most relevant for color vision… Complexity or Purity Different wavelengths hue multiple of wavelength saturation brightness Different intensities Amplitude ≈ Intensity Wavelength
Why light? Vision as a distance sense The eye captures light reflected from objects and forms an image on the back of the eye. How “should” the image be formed? surfaces, substances source Some light gets to eye reflected scattered absorbed
Camera Obscura (Alhazen) Limitation : Doesn’t let in much light—blurry image Problem : Spatial ordering of rays reflected from the object have to be recovered from the divergent light. box with a pinhole as the eye Solution #1 : Allow one ray from each part of the object into the eye.
Limitation : Clear focus depends on the power of the lens and angle of divergence of light rays. Problem : Spatial ordering of rays reflected from the object have to be recovered from the divergent light. … while letting in enough light for a clear image. Allows larger hole more light sharper image Solution #2 : Use a lens that refracts light so that rays from the same point on the object converge .
Limitation : Clear focus depends on the power of the lens and angle of divergence of light rays. Problem : Spatial ordering of rays reflected from the object have to be recovered from the divergent light … while letting in enough light for a clear image. Different distance of object from eye changes angle of light rays Out of focus for that lens. Solution #2 : Use a lens that refracts light so that rays from the same point on the object converge .
… of objects at varying distances. Problem : Spatial ordering of rays reflected from the object have to be recovered from the divergent light …while letting in enough light for a clear image Solution #3 : Lens with variable optical power changes shape to accom- modate the distance of the object to the size of the eye.
The eye as a chamber for capturing light Optical parts Structures for gathering and focusing light What properties should the eye have? Translating parts Structures for copying light and sending signals
Light is focused on light-sensitive photoreceptors of retina that convert or transduce physical energy into neural activity
Lens shape can be changed to accommodate to the distance of an object for focusing on the back of the eye—the retina —centering on the fovea
Fluid in eye keeps its shape from changing so that focusing properties are reliable
Focusing-relevant features highlight the importance of the retinal image
cornea iris lens pupil optic nerve retina fovea
Retinal Image is Starting Point for Vision … and we have two Visual Fields defined relative to fixation x : L VF projects to right side of each eye and on to the Right Hemisphere LVF RVF Right Visual Cortex
Retinal Image is Starting Point for Vision … and we have two Visual Fields defined relative to fixation x : R VF projects to left side of each eye and on to the Left Hemisphere Right Visual Cortex Regions of left eye correspond to regions of right eye At some point we have to (re)connect visual fields. L VF projects to right side of each eye and on to the Right Hemisphere LVF RVF Left Visual Cortex
Philosophy : Begin with objective physical properties
Physics : Intensity, wavelength of reflected light
Physiology : Brightness, color but not 1:1
Phenomena : Product of mental computation
Physics Psycho- Anatomy & Algorithms physics Physiology Goals: Get copy of world inside head Difficulty: Pointillisitic nature of light (and sensations) Solution & Problem: Eyes capture images Pervasive Themes world energy sensations pattern perception
Before we had techniques to see cells, we had behavioral data: Go from bright light into dark room—can’t see at first Improves for 5 min., levels off… improves again for 15–20 min. Kink in function is clue 2 functions 2 functions 2 types of photoreceptors 2 job descriptions: Transducing the image
Blindspot: no receptors because the optic nerve leaves the eye.
fewer in number
Rods no. of receptors per square mm What are consequences? What are consequences? So does shape: rods and cones Cones
Return to dark adaptation curves for hints very little light required more light required Differ in Sensitivity 2 weak signals that are separate remain below threshold of next cell less sensitive 2 weak signals that are connected can exceed threshold of next cell more sensitive
many:1 with later cells
1:1 with later cells
Ø ! Ø Ø Ø minutes in dark Threshold (minimal visible light intensity) Ø Ø ganglia ganglia
How a pattern is experienced depends on where it projects on the retina Is there a cost to pooling signals? Is there a benefit to keeping signals separate? detail is missed: less acuity detail is noticed: greater acuity
Array of ≈ 130,000,000 photoreceptors converts the retinal image into a neural image to be transmitted to the brain. But… How good is mapping between world and experience? Which of these problems get fixed higher up? How are they fixed?
image is upside down
different parts of retina have different sensitivities
Array of ≈ 130,000,000 photoreceptors converts the retinal image into a neural image to be transmitted to the brain. But… Receptors outnumber cells in the next layer pooling of information, editing, altering before signals are passed along How good is mapping between world and experience? Which of these problems get fixed higher up? How are they fixed? mechanisms rules
image is upside down
different parts of retina have different sensitivities
Ganglia respond to receptors, not to light (register differences in light) Examine the language of ganglia: action potentials All or None Cells beyond receptors condense and reorganize data
130,000,000 receptors 1,000,000 ganglia
many, many rods : 1 ganglion ; 1 (or a few) cones : 1 ganglion
a lot of editing
What kind? What kind of stimulus does a ganglion prefer? Use single cell recording with electrodes
a still eye to keep stimulus where you want it.
stimulate various areas of the retina
see effect on a particular ganglion.
reveals editing oscilloscope amplifier microelectrode time (sec) voltage
Without stimulus there is a base level of spontaneous activity . Task: Find the region on the retina whose stimulation will change the resting level (higher or lower) of Ganglion “A”. How: Scan retina with stimulus to see where ganglion’s activity is affected ( where matters ) Homogeneous gray spontaneous activity. Spot of light greater than spontaneous activity Dark spot in area less than spontaneous activity Within area greater than spontaneous activity Outside area less than spontaneous activity
Spontaneous firing rate is affected up or down concentric ON/OFF regions Ganglion cell’s receptive field (a collection of retinal cells) What happens with light outside the ON/OFF region? What is experienced depends on where it hits retina Assessing various ganglia yields a receptive field map overlap, producing a mosaic covering the whole retina (also OFF center/ON surround cells) “ ON” response “ OFF” response Distribution of concentric ON/OFF regions arises from connections among preganglion collectors spontaneous rate excited rate inhibited rate spontaneous rate
ON center “prefers” light; surrounding OFF circle “prefers” dark
antagonistic responses from center and surround lateral inhibition patch of light over entire field patch of dark over entire field Increased activation from ON center countered by decreased activation from OFF surround. Decreased activation from ON center countered by increased activation from OFF surround.
Dark edges over OFF surround with light on ON center vigorous response: whole receptive field is getting its preferred stimulus detects and accents light/dark boundary Edges are preferred by this kind of cell. illuminate only the center dark bar on the surround What pattern on the retina would be preferred by a Center/Surround cell?
Consequences of antagonistic relationship between center and surround same response to dif. intensities dif. responses to the same intensity Constancy Illusions Good mapping in a limited range? Intensity of Center Response Intensity of Center Response Intensity of Center Response
From what we know about acuity, how should size vary in different areas of the retina? large in periphery; small near fovea Many:1 vs. 1:1—Receptive fields vary in size Physiological mechanisms are recovering edge and size information building blocks of meaning. Small receptive fields respond best to small objects; large to large beginning of object size extraction . From what we know about preferences of receptive fields, how should they respond to objects of different sizes?
Acuity : smallest high contrast detail perceived at a given distance Receptive fields have consequences for the kinds of patterns that go into Unconscious Inferences. What letter is this? F E A H O D P R Identification Acuity Can you see this? Detection Acuity 1 or 2? Pattern or gray? Resolution Acuity K
Note disparities between and made possible by lateral inhibition — mechanism that highlights edges through sideways connections among cells. Illusory consequences illustrate how it works. dependence on “irrelevant” conditions (e.g., distance) The “private line” from foveal cones to the brain provides fine detail… … but it’s neurologically expensive receptive field organization is important
Mach bands do not exist physically wouldn’t be picked up by a photometer
Physiology imposes its character on the input
A physical contrast —a border— that does exist is accentuated
Machinery can be inferred from experience
stimuli ≠ perception of those stimuli Lightness Contrast Implies interaction in connections between neighboring cells: some signals boosted, some signals reduced : Central squares reflect same amount of light. : The darker the surround, the lighter they look . : Central squares reflect same amount of light.
A LEFT looks darker than A RIGHT Initial “strength” of signals (registered by rods) A LEFT = A RIGHT B LEFT > B RIGHT
excitatory or inhibitory
Signal from B LEFT inhibits signal from A LEFT lateral inhibition B A B A If signal from B exceeds threshold of laterally connecting cells, signal from A will be reduced Signal from B RIGHT does not affect A RIGHT Consequently, A LEFT < A RIGHT
ganglia pool information , change from what is given
copies (which are inadequate )
Evidence for assumptions of Indirect Realism
separate receptors , connected into receptive fields
disconnected sensations, mosaic
eye as camera , receptors as film
Same mechanism is destructive and constructive
It distorts relative to Illusions
It enhances the detection of an important feature of the world edges
sends excitatory signal when stimulated sends inhibitory signal when stimulated front view
many:1 with later cells
1:1 or few:1 with later cells
Receptive fields care about size & shape… … but not orientation. Orientation influences what objects mean Pool some more. To overcome mosaic, connect receptive fields. ” reduced rate: stimulus hits both excitatory and inhibitory cells
Receptive fields overlap Across a collection of receptive fields, orientation matters Collection reports to cells in the cortex . They have receptive fields too Record from 3 cortical cells Cortical cells do edge detection but more cleverly Cortical receptive field shapes are not uniform Hubel & Wiesel (1959, 1962; Nobel Prize 1981)
stimuli must be positioned appropriately maximal response to stimuli of a particular orientation ±15°. Simple cells receptive fields look like their preferred orientations response rate response rate
Complex and Hypercomplex cells Some cells prefer movement of those features in a particular direction
don’t care about precise placement
larger receptive fields
no clear ON-OFF regions
prefer moving stimulus
combinations of features
Measure activity in cell that prefers downward moving horizontal 3 cm line Provide some information about where, what, and what’s it doing.
Are Cortical Cells Feature Detectors? Rate of firing is the only vocabulary—how is ambiguity resolved? Reduced response if orientation or size or motion is not exact which is it? More complex response is still ambiguous
Response is ambiguous
Respond maximally , not exclusively, to their feature
ambiguity at level of single cell direction orientation response rate response rate
which qualitative properties are preserved, lost, distorted
Physical Psychological light or an object detection thresholds differences in intensity, etc. jnd s , acuity Intensity, reflectance constancy, contrast different wavelengths not distinguished in dim light X-ray, infrared visible spectrum gives us variables builds from elements meaningless adds meaning Strategies of Indirect Realism
Reality question is emphasized in color perception.
Objects have no color.
Reflected light is no more colored than are radio waves!
To appear colored , reflected light must be picked up by the right kind of eye and nervous system .
Color is a psychological thing.
Which level is real, the simple end of the hierarchy or the complex end? The variables or the experiences? The first representation— levels of contrast —is meaningless and must be reconstituted to get more specific and more meaningful. Is an edge real? Visual stimuli are built hierarchically from simple to complex surface pigment shadow
Light rays, paints, filters, etc. merely use radiant energy selectively.
Color is a product of the visual system, not the visible spectrum.
wavelengths, not colors produce; reflect, absorb; transmit how our retinal physiology responds
White light decomposed into s p e c t r a l c o m p o n e n t s refracted by a prism and split into rays of different wavelengths. amount of refraction determined by wavelength Newton (with some refinements) Nonetheless, color sensations are related in consistent and measurable ways to physical features of light infrared (not visible) red orange yellow green blue violet ultraviolet (not visible)
Complexity or Purity Different wavelengths hue multiple of wavelength saturation brightness Different intensities Amplitude ≈ Intensity Wavelength
How do we respond to different kinds of light? Pure #1 + Pure #2 = Composite
equivalence is due to nervous system
Different things with identical neural effects: metamers
pure vs. composite light If Pure #1 + Pure #2 + … = White then 1 & 2 are complementary Components “cancel” or “blend” psychologically but not physically spectral components would still be detectable to instruments. Both are white
: wavelength : hue You can add pure colors and get one that’s not a spectral color no characteristic wavelength 530 650 Metamers tell us how to organize the optics : Complementary colors are opposites in some sense 580 460 A color circle, but… 600 O R G B Y ??? P 490 B - G G - Y 490
Other experiences suggest organizations more elaborate than a circle : intensity : brightness What happens when there is more or less light? What does the color look like? The higher the %white the less saturated a color will look. The higher the % other wavelengths, the less saturated a color will look. : spectral purity : saturation blue . . . heather blue . . . gray green . . . heather green . . .gray red . . . pink . . . gray Maximal at moderate intensities only
Colors on opposite sides gray Broadest portion appears at medium lightness. Any cross-section color wheel for a particular lightness Wavelength + Intensity + Purity Color experience all colors can be obtained from a few primaries tells us about the physiology of color perception The Color Solid brightness white black
A single wavelength is matched by different amounts of 3 primaries indicate limits of the information senses pick up indicate how the brain uses that information Metameric Matching : Present a target color and have observer match it with a mix of others. Would 1 cone type work? Or 1 cone per color? 3 primaries Comparison x R + y G + z B 1 wavelength Test Field C =
Young: 3 specialized cones each acts as a channel responsive to specific spectral composition. Retina as mosaic of independent triads of cones Light at each retinal point analyzed into 3 components
Return to experience:
Why is there no reddish-green ?
Why is color blindness a matter of confusions ?
most common is red with green
color afterimages show same combinations
S M L Young-Helmholtz (and Newton and Maxwell) Tri-chromatic Theory Helmholtz: 3 types of cones, each with a graded sensitivity function 100 0 400 500 600 Wavelength % of Max. Absorption What is the origin of the pairings?
Trichromatic theory not the whole story Color afterimages Color blindness comes in pairs
Hue determined by relative activity of R - G and B - Y ;
lightness determined by activity of B - W cells;
saturation by which kinds of cells are most active:
Complementary colors cannot coexist because a pair cannot respond actively to both
Color deficiencies are characterized by pairs
DESIGN OF RETINA TO OPTIC NERVE To Brain light optic nerve fovea retina RODS CONES BIPOLARS GANGLIONS LIGHT LIGHT
A NEURAL SYSTEM OF OPPONENT PROCESSES IF + > – , THEN “BLUE” IF – > + , THEN “YELLOW” IF + > – , THEN “RED” IF – > + , THEN “GREEN” + – – CONES GANGLION CONES GANGLION – + + FOR BOTH OPPONENT PROCESS SYSTEMS: IF + = – , THEN “GRAY” (ACHROMATIC)
Wavelength info at retinal level; feed into opponency Fits into the overall theme of the perceptual system missing physical detail, restoring lost structure, making things up as it goes along. But it is also an example of the visual system getting what it needs: There is a biological advantage to seeing color. Note: We’ve really been limited to sensations . Perception is still to come. Color coding is a two-stage process. Puzzle: All this happens inside eyes and brain. How do we experience the world as outside?
Edges are a specialty of the visual system. Specialty implicates a mechanism for perceiving separable objects. • Neurophysiology: primitives hierarchical combos Old theories illustrate persistent issues analytic introspection : specialized technique for observation stimulus error: mistaking the object for experience Sensations vs. Perceptions Structuralism was a kind of mental chemistry. Elemental structures combine to build perception What does the visual system start with? What are the elements? What do you really see, without interpretation? No, really No, really No, really
How do I know that this pattern is a hand? Examples of types of representations and types of computations Analysis must provide components abstract enough to match stored representation. More candidate primitives
and their relationships
applied to S P & to stored representation
Or this? Or this?
Keep track of vertex-connected surfaces eliminate those that are inconsistent For complicated—natural—scenes, occlusion is a problem Even if these are identified as cylinders, how do we know they are part of the same object? We need rules about what’s likely. … with what you know about objects Given experience, assign to S P the S D that is most likely to have caused it. Overcomes problem caused by occlusion corner of front surface not always 3-D corner of one object not always
Different neural activity = different forms… HOWEVER… Form (object) recognition still presupposes a solution…an internal representation. Still doesn’t answer the how question. How (where) does perception occur? =
Defects (e.g., gaps) in RI would be preserved in brain
Structuralism ignored interactions in nervous system play organizing role The Gestaltists Why do things appear as they do? Gestalt is German for whole form “ The whole is different from the sum of its parts.” Principles of Organization encourage grouping, segregation form emerges Yes! But what are they? i. They are what they are? iii. The brain processes are what they are? ii. S P are what they are? What do you see? is 9 circles 1 S P 2 experiences
Grouping or organization is not in the stimulus .
Seen as 3 pairs of lines
S P does not dictate that over
Seen as intersecting shapes
S P does not favor
The Law of Proximity does
Seen as alternating columns
S P does not dictate that over
The Law of Similarity does The Law of Good Continuation does
Seen as triangle in front of 3 circles
S P does not dictate that over
The Law of Closure does or or over
What counts as a form or grouping distinct from a background? In general, Simplicity 3-D or 2-D?
What is the figure can be complicated Ambiguous Figures: For same S D and same S P , two percepts are possible How can you have 2 simultaneous, incompatible representations of the same thing?
Figure-ground is reversible
Can be shifted by attention
Figure vs. Ground: What does the edge belong to?
Of the alternatives allowed by the proximal stimulus… infer the more likely. The Helmholtzian Solution: Use knowledge of which configurations are likely: Principle of maximum likelihood. Make Unconscious Inferences about the world. Contrast detection is not enough identify which form the edge belongs to ( Pattern recognition presupposes a solution) Figure vs. Ground: What does the edge belong to?
Structuralists emphasized identifying primitives as adding or associating sensations… theirs were too subjective, too qualitative Gestaltists emphasized emergent properties or organizing through grouping laws theirs were descriptive, not predictable. But, how it looks ≠ what it is. Form requires further processing. Teacher through your glasses? Teacher in your locket? far near For example, distance matters
Pattern recognition = ƒ(distance, size, shape) How do we know both relative distance and absolute distance? Back to Helmholtz and Unconscious Inference How does S P come to indicate a particular S D given that S P is 2-dimensional and, therefore, ambiguous? Reasonably reliable in a Helmholtzian what-is-normal sense is provided by cues RI for large, far objects = RI for small, near objects Is there reasonably reliable structure that might be used to solve Molyneux’s problem? A B C D
II. Attempts to simulate depth: pictorial cues I. Berkeley “on-line”: oculomotor cues convergence accommodation Distance Perception
Become associated with properties of S D through experience.
Aspect of S P X X X X
III. 2 eyes that receive slightly different views: binocular disparity Left thumb behind, Right thumb in front; Both far away Thumbs close together Amount of disparity indicates relative distance, separation Thumbs far apart Both up close R R L L L R L R
Motion Based Cue for Depth: Ever look out the window while riding in a car? Direction of Travel Objects in the foreground move by faster than objects in the background - Very distant objects appear to remain stationary Motion Parallax
Size Perception But there’s ambiguity… II. Familiar Size pumpkins are larger than apples…
except for small pumpkins
compare to similar objects in the scene:
III. Relative Size
Unconscious Inference uses knowledge about what’s normal RI pumpkin = RI apple Which is bigger? RI pumpkin > RI apple pumpkin is larger than apple I. Retinal Image Size : Larger objects project larger RI
Knowledge is needed to make sense of ambiguous cues to attribute the proper cause to your S P . Helmholtz’s Unconscious Inference In natural scenes cues co-occur strengthen the impression of depth & size. In experiments, cues are manipulated alter the impression of depth & size.
Strategy: isolate cues or put them in conflict to assess
cues’ relative potency
gain insight into normal processes, algorithms
We perceive constant object properties despite variability in the S P that is our contact with them. Perceptual Constancies
Size Perceived = ƒ( RI Size , Distance Perceived ) Tested by Holway & Boring (1941)
target disk on L
Indicate size by method of adjustment Targets chosen to project same RI @ every distance Percept-Percept Coupling
response on R
Manipulate available cues to distance and assess effect on perceived size :
fewer cues to distance more reliance on RI
Breakdown of Size Constancy
F M S P Actual Size Perceived Size constancy slope = 1 retinal size slope = 0 Full Cue Monocular Static Peephole
Cue: S P:A = S P:B Perc’d size is derived from perc’d distance A looks bigger than B A B A = B Cue: linear perspective says “ A is farther than B ”
S P1 ≠ S P2 Percept @ p1 = Percept @ p2 Shape Constancy Ex. II. Perceived Shape is unaffected by perspective p1 p2
Appearance is affected by interpretation! Parallelograms look similar in size and shape (one is rotation of other) Shape Perc’d is derived from distance Perc’d Adding distance cues changes inferred shape. percept-percept coupling Manipulate depth cues & assess consequences for Shape Perc’d .
Fixing S P is logically prior to pattern recognition . What form is it? Fundamental problem is normalization of image for memory.
Compare to stored representations
How abstract can the representations be?
How tolerant are matching processes?
How would a representational account handle movement? Objects in the world often move…they are not not static!!
Motion Perception Perception Apparent (Stroboscopic) Movement Do we see things as they are because of the proximal stimulus? No Do we see things as they are because of brain states? Yes Or… A temporal property (change over time) is derived from a succession of static retinal images. t 2 t 3 t 1 Physical Event
Interpret with respect to likelihoods . Apparent motion of the disk induced by assumption that enclosures don’t move. The same assumption would underlie our experience of non-illusory motion, too. Again, illustrated by an illusion : “induced motion”
BUT… Helmholtzian account: compare RI with commands to muscles Did I tell myself to move?
ambiguity if I’m being moved passively
ambiguity if we’re both moving
Puzzle: How is leftward movement of something distinguished from rightward movement of me (or my eyes)? 1 2 3 4 1 4 2 3 Stimulation of successive retinal locations motion 1 2 3 4 Same pattern for car moving to left and me moving to right. 1 2 3 4
The Phenomena of ATTENTION: Selective Listening WHAT IS KNOWN ABOUT UNATTENDED? Only physical characteristics (speech like sounds). Not meaning. “ unattended” “ attended” DICHOTIC LISTENING I cannot tell a lie Never kill a snake SHADOWING I cannot tell a lie COCKTAIL PARTY EFFECT Except when important or relevant (e.g. name) The ever present Unconscious at work yet again….
Indirect Perspective of Perception Assumes: Both relinquish the responsibility of perception to an “internal”, “mental”, knower… a homunculus … who organizes and isolates cues and compares percepts and representations. Proximal Stimulus Meaningless Sensations Association/Cues Distal Stimulus Incomplete “ Percepts” Incomplete “ Percepts” Perception Unconscious Inferences, information processing, Laws of organization