1. Artifact Rejection and Noise Removal
• We eliminate the trials with artifacts in measurement of pupil size based on visual inspection.
• Because of the slow dynamics of the pupil changes, we used a low-pass filter that allowed the
signals with a frequency lower than a certain cutoff frequency (f = 4 Hz).
Normalization Procedure
• We subtract the baseline activity (mean amplitude of 300ms fixation) from the stimulus evoked
pupil response.
• To make the two distributions comparable we normalized the pre-processed data. For that, we used
z-scores to convert all the samples to a common scale.
Perceptual modulation of pupillary reflex in macaque monkeys
Rea Antoniou1,2,Shervin Safavi1,3, Vishal Kapoor1,3 ,Nikos Logothetis1,4 Theofanis Panagiotaropoulos1,5,6
1 Max Planck Institute for Biological Cybernetics, Tübingen, Germany; 2 Aristotle University of Thessaloniki, Thessaloniki, Greece; 3 IMPRS for Cognitive and Systems Neuroscience, Tübingen,
Germany; 4 University of Manchester, Manchester, United Kingdom, 5 University of Leicester, Leicester, United Kingdom;
6 King’s College London, London, United Kingdom
Main References
Conclusion
o Naber, M., Frässle, S., & Einhäuser, W. (2011). Perceptual Rivalry:
Reflexes Reveal the Gradual Nature of Visual Awareness. Plos One.
Retrieved from doi:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.002091
o Bárány, H., Halldén. (1948). Phasic inhibition of the light reflex of the
pupil during retinal rivalry. J.Neurophysiology, 11 pp. 25–30.
Data Structure
Introduction
• Pupillary light reflex controls the diameter of the pupil in response to the intensity of light.
• Consensual response is the change in pupil size in the eye opposite to one is stimulated.
Pupil contraction Pupil dilation
• Pupillary response is not purely light reflexive but it can also be mediated by perception.
• Binocular flash suppression (BFS) and binocular rivalry (BR) are two paradigms of studying
conscious visual perception for humans and non-human primates.
• In humans, it has been demonstrated that pupil dilates during spontaneous perceptual transitions
(for example during Binocular Rivalry).
• However our knowledge about pupillary perceptual reflexes in macaque monkeys is limited. Since
macaque monkeys are considered as a good animal model for understanding conscious visual
perception, it is important to characterize these reflexes.
• In this study we used Binocular flash suppression in macaque monkeys to characterize
pupillary perceptual reflexes.
Pre - processing
• Pupil diameter was sampled at 200 Hz during the task using an eye tracker
• Macaque monkeys were exposed to Binocular Flash Suppression (depicted in the figure below):
A paradigm of binocular visual stimulation during which:
a) a stimulus flashed in one eye is dominant while,
b) a disparate stimulus initially presented in the other eye is suppressed.
Suppression vs. Dominance
• Our results suggests that during ambiguous binocular visual
stimulation pupil contraction is stronger compared to monocular
visual stimulation.
• Therefore, the same perceptual experience may lead to significant
differences in pupil diameter depending on the context of visual
stimulation (ambiguous binocular vs monocular).
• Pupil diameter is modulated individually for each eye depending on
the dominance or suppression (in BFS) and presence or absence (in
PA) of a visual stimulus.
• Luminance alternations in the nature of the stimuli could play a
significant role in future research since they can lead to different
pupil reactions.
• Since recordings were exclusively on the right eye, a potential
experiment recording both eyes may provide insights into the
mechanisms of pupil modulation during ambiguous binocular
stimulation.
Experimental Setup
Ambiguous vs. Non- ambiguous stimulation
Both traces express the pupil reaction of the right eye during BFS in the following
conditions:
Condition 1: Until 1000 ms the right eye is unstimulated and after 1000 ms a stimulus
flashes and becomes dominant.
Condition 2: The right eye starts being stimulated and dominant. After 1000 ms the
second stimulus flashes to opposite eye and the right eye becomes suppressed.
1) At 1000 ms a perceptual conflict is observed.
2) After 1000 ms the dominant eye shows a bigger contraction compared to the
suppressed one.
3) After τ = 250 ms pupillary reactions to suppression (green) and dominance (red)
are observed.
The figure above shows pupil modulation of the right eye during both BFS and PA
conditions:
Condition 1: Until 1000 ms the right eye is dominant and after the input of the second
stimulus in the opposite eye the right eye becomes suppressed (BFS).
Condition 2 : Until 1000 ms the right eye is stimulated (PA) and afterwards the
stimulus is being removed.
1) The pupil of the suppressed eye in BFS condition contracts more compared to the
pupil of the non stimulated eye in PA condition (comparing red and green traces
after 1300ms).
2) Sensory or perceptual ambiguity (or both) seem to play an important role in pupil
modulation.
The figure below depicts pupil modulation of the right eye during
different conditions of PA:
Condition 1: Until 1000 ms the right eye is dominant due to the
presence of a stimulus whereas afterwards the stimulus is being
removed.
Condition 2: Until 1000 ms the right eye is unstimulated and after the
input of the stimulus the right eye becomes dominant.
 The stimulated eye shows earlier contraction compared to the
contraction observed in the non stimulated eye (consensual
response).
Input of the second stimulus.
τ
Input of the second
stimulus.
• The above figure depict a pupil size time series from an arbitrary trial (without pre-processing).
• We did the analysis on the stimulus evoked part of the signals (after 300ms).
Fixation
period
Presentation of the
first stimulus
Presentation of the
second stimulus
Delay in the pupil response
of the suppressed eye
Consensual pupillary responses
• In the same sessions animals were exposed to monocular visual stimulation, so-called Physical
Alternation (PA).
Time (ms)
PupilSize
(au)