We present new psychophysical estimates of the size of the rod pool for bleaching adaptation in the human retina. We estimate that at 5 deg nasal eccentricity in the human retina the size of the adaptation pool for rods is between 5 and 7.5 min arc. This estimate is compatible with the extent of the dendritic spread of rod bipolars located in this region of the primate retina and with the area occupied by roughly 50 rods in this parafoveal region of the human retina. Thus a candidate for the site of adaptation is the bipolar cell whose receptive field is comprised of approx. 50 rods. These estimates represents the lowest measurements to date of the size of the adaptation pool for rods.

We investigated the spread of bleaching adaptation for human cone vision in the central fovea and at an eccentricity of 5 deg in the nasal retina. Cone thresholds measured after adaptation to a grating bleach were compared to those measured after a uniform bleach. We conclude that the foveal and parafoveal cone systems show excellent localization of the effects of adaptation. For areas 2.5-5 min removed from the bleach, our measurement show only small sensitivity losses amounting to between 0.10 and 0.25 log unit elevation in threshold, after taking account of optical scatter.

Infants’ ability to anticipate the actions they observe is thought to be a critical skill in early social-cognitive development. A considerable body of research has demonstrated that infants can anticipate observed actions from a variety of cues in different kinds of visual contexts. However, most of this work has relied on screen-based eye-tracking paradigm using highly controlled computer stimuli. Less is known is known about whether and how infants anticipate live actions in natural settings. One prior study demonstrated that infants did anticipate their parents’ actions during live, free-flowing parent-infant play, though they did so infrequently. Using head-mounted eye-tracking, the current study aimed to build upon this work by exploring whether infants make gaze predictions while observing their parents perform an everyday activity in a home-like environment—assembling several peanut-butter and jelly sandwiches. Preliminary findings reveal that infants anticipate their parents’ actions at relatively high rates, indicating a close coupling between parent actions and infant gaze. Rates of prediction did not change over the course of the observation, suggesting that infants already possess prior knowledge of the action sequence structure that they utilize to successfully predict their parents’ ongoing actions.

Recent successful robotic models of complex tasks are characterized by use of deictic primitives and frequent access to the sensory input. Such models require only limited memory representations, a well- known characteristic of human cognition. We show, using a sensori-motor copying task, that human performance is also characterized by deictic strategies and limited memory representations. This suggests that the deictic approach is afruitful one for under- standing human brain mechanisms; it also suggests a computational rationale for the limitations on human short term memory

We are interested in a functional account of how capacity constrains memory use in natural, ongoing behaviors, and in how visual memory demands can be reduced through the use of what we have called perceptual pointers, or deictic codes. Here, we ask whether, with experience, participants can restructure task representations such that single fixations can point to more and more complex chunks of information. We tracked eye movements as participants copied simple model patterns which were presented with different frequencies. At first, participants made multiple fixations to individual pattern components. As patterns were presented repeatedly, model inspections were reduced substantially. This suggests that participants formed more compact representations of the patterns with experience, allowing single fixations to point to larger chunks of information. We also propose that deictic codes provide a short-term store analogous to the visuo-spatial scratchpad or articulatory loop. When the task was structured such that a separate visual search was required for each model component, much less learning was observed than when fixations to known locations were required, suggesting deictic codes were disrupted by active visual search.

Coordination between visual and motor processes is critical for the selection of stable footholds when walking in uneven terrains. While recent work (Matthis et al. in Curr Biol 8(28):1224-1233, 2018) demonstrates a tight link between gaze (visual) and gait (motor), it remains unclear which aspects of visual information play a role in this visuomotor control loop, and how the loss of this information affects that relationship. Here we examine the role of binocular information in the visuomotor control of walking over complex terrain. We recorded eye and body movements while normally-sighted participants walked over terrains of varying difficulty, with intact vision or with vision in one eye blurred to disrupt binocular vision. Gaze strategy was highly sensitive to the complexity of the terrain, with more fixations dedicated to foothold selection as the terrain became more difficult. The primary effect of increased sensory uncertainty due to disrupted binocular vision was a small bias in gaze towards closer footholds, indicating greater pressure on the visuomotor control process. Participants with binocular vision losses due to developmental disorders (i.e., amblyopia, strabismus), who have had the opportunity to develop alternative strategies, also biased their gaze towards closer footholds. Across all participants, we observed a relationship between an individual's typical level of binocular visual function and the degree to which gaze is shifted toward the body. Thus the gaze-gait relationship is sensitive to the level of sensory uncertainty, and deficits in binocular visual function (whether transient or long-standing) have systematic effects on gaze strategy in complex terrains. We conclude that binocular vision provides useful information for locating footholds during locomotion. Furthermore, we have demonstrated that combined eye/body tracking in natural environments can be used to provide a more detailed understanding of the impact of a type of vision loss on the visuomotor control process of walking, a vital everyday task.