During an eye blink, visual input is disrupted while objects in motion continue to change in position. How does this temporal occlusion affect our ability to accurately perceive motion and time? We carried out two experiments to investigate perception of motion trajectories at the time of a blink. In Experiment 1, we presented participants with a moving stimulus on a circular trajectory around fixation that disappeared upon detection of a blink, and instructed them to indicate the perceived location of the stimulus at the point of disappearance with a mouse click. In Experiment 2, participants were presented with a similar moving stimulus that jumped either backward or forward by a variable amount during a blink. Participants were instructed to indicate the perceived direction of the jump. In control conditions the stimulus would disappear (Experiment 1) or jump (Experiment 2) while participants’ eyes remained open. In Experiment 1, we observed significantly greater overshoot of motion on blink trials, with the last perceived stimulus position shifted forward by a constant distance into the period of occlusion during the blink. In Experiment 2, participants perceived a backward jump that occurred during a blink as continuous, consistent with the notion that time during a blink was perceived as ~60-100 ms shorter than in actuality. These results suggest eye blinks are partially filled in with extrapolated trajectory information, and that elapsed time during a blink is perceptually compressed (Duyck et al., 2015, J Vision 15, 370; Irwin & Robinson, 2016, J Exp Psy Hum Perc Perf 42, 1490-6).
The ArtScience Museum at Marina Bay Sands in Singapore has an exhibition on the amazing works of Dutch artist M.C. Escher. Anybody with an interest in visual perception and illusions should use the opportunity.
We did so with the lab at the end of the semester.
Katie spent 8 weeks in the lab this summer to study adaptation to dynamic stimuli. She’s now back at the University of Nevada, Reno to finish up her PhD thesis, and we’ll continue to collaborate on the project we started here.
Hannah spent the last 9 months in the lab and collected lots of data on perceptual consequences of eye blinks. More on that soon :). She’s now at the University of Sussex in Brighton, England to study for her Masters degree in Cognitive Neuroscience.
Gerrit presented some recent findings from his studies on eye blinks (with co-author Thérèse Collins). See abstract below:
Single-blink adaptation of gaze direction to correct for oculomotor errors
When a fixation target is displaced repeatedly during eye blinks, the oculomotor system adapts: when a target is moved laterally by a fixed step size during repeated eye blinks, the initial gaze direction after each eye blink becomes biased towards the new target positions, without the subject noticing. Previously reported for repeated identical displacements, here we show that this adaptation of gaze can also occur for random target steps, and is evident after just one blink. Observers were instructed to fixate a target dot on the screen. We detected eye blinks in real-time and used them to trigger random target jumps left or right (between 0.1 and 1.0 degrees). We recorded the first gaze direction after each eye blink, and observers reported the perceived direction of each jump. The change in gaze direction from one blink to the next correlated with the retinal position of the target after the previous blink. This correlation was reduced, when observers perceived the previous jump accurately. This is evidence for a fast-acting adaptive mechanism: when visual changes during blinks are not perceived as object motion, the oculomotor system tries to compensate for previously experienced errors due to oculomotor noise.
Minh is a Neuroscience student from UCL and will spend the next 8 weeks in the lab to learn about visual psychophysics and work on experiments on motion adaptation in natural stimuli. Welcome Minh!
Our lab is presenting some recent results at the Asia Pacific Conference on Vision (APCV 2016) in Perth, Western Australia.
Aaron is showing results of his experiments on a novel “motion smoothness aftereffect”, and Gerrit is presenting results showing that gaze direction can adapt to stimulus displacements after a single eye blink.
Abstracts are included below:
Adaptation to velocity profiles of random moving dots: A motion “smoothness” aftereffect
Jit Wei Ang, Gerrit Maus
Previous reports of motion adaptation range from low-level adaptation of speed and direction to high-level adaptation of biological motion. However, little is known about potential mid-level processes that could contribute to higher-level aftereffects. Using random dot kinematograms, we adapted observers to two velocity profiles with matched average speed: sinusoidal variations in velocity (“smooth” or constant speed with abrupt direction reversals (“jerky”). Subsequently, we tested perception of different velocity profiles that ranged from smooth to jerky by either morphing the smooth and jerky profiles with a “neutral” (Gaussian) profile, or by varying the ratio of smooth and jerky dots. In a 2AFC task, observers judged which of two differently adapted stimuli looked smoother. All observers judged subsequent stimuli as “jerkier” after adapting to “smooth” motion and vice versa. Adaptation to different velocity profiles is unlikely to depend on lower-level adaptation, but might contribute to higher-level aftereffects, as in biological motion.
Adaptation of gaze direction following single eye blinks
Gerrit Maus, Therese Collins
When a target is displaced repeatedly during eye blinks, the oculomotor system adapts: the initial gaze direction after each eye blink becomes biased towards the new target position, without the subject noticing. Previously shown for repeated identical displacements, we now present evidence of such gaze adaptation after random target steps, and after just one blink. Observers were instructed to fixate a target dot. Eye blinks triggered random target steps left or right (between 0.1 and 1.0 degrees), and observers reported the perceived direction of each step. The change in gaze direction from one blink to the next correlated with the retinal position of the target after the previous blink. This correlation was reduced when observers perceived the previous step accurately. This is evidence for a fast-acting adaptive mechanism that compensates for oculomotor noise when visual changes during blinks are not perceived as object motion.
Gerrit (with co-authors Mandy Chen from Beijing and Rachel Denison from New York) presented a poster on how illusory occlusion due to filling-in at the blind spot can influence depth perception (abstract here).
Undergraduate Ann Chu Ning was involved in a study on local and global sources of noise for motion integration, that was presented as a talk by Prof. Alan Lee from Hong Kong (abstract here).
Motion information helps to fill in the blind spot. Although we do not receive bottom-up input from the region of the retina corresponding to our blind spot, we do not see a “hole” there, but information from the surrounding area gets “filled in”. This process, however, is limited. Here we show that motion information from near the blind spot helps to fill in spatiotemporal information.
We spend the last two months buying furniture, setting up equipment, calibrating monitors etc., so that we can say now with not a little pride: The psychophysics lab is up and running! Have a look at some pictures here
