Atsushi Noritake

Perisaccadic perception of continuous flickers

To realize perceptual space constancy, the visual system compensates for the retinal displacement caused by eye movements. It has been reported that the compensation process does not function perfectly around the time of a saccade--a perisaccadic flash is systematically mislocalized. However, observations made with transient flash stimuli do not necessarily indicate a general perisaccadic failure of space constancy. To investigate how the visual system realizes perisaccadic space constancy for continuous stimuli, we examined the time course of localization for a perisaccadic 500 Hz flicker with systematic variation of the onset timing, the offset timing and the duration. If each flash in the flicker is localized individually in the same way as a single flash, the apparent position and length of the flicker should be predicted from the time course of mislocalization of a perisaccadic flash. However, the results did not support this prediction in many respects. A dot array (of half the length of the retinal image) was perceived when the flicker was presented during a saccade, while only a single dot was perceived when the flicker was presented only before or after the saccade. A flash in a flicker was localized at a different position, depending on the onset timing, the offset timing and the duration of the flicker, even if the flash was presented at the same timing to the saccade. In general, our results support a two-stage localization in which the local geometrical configuration is first generated primarily based on the retinal information, and then localized as a whole in the egocentric or exocentric space. The localization is based on the eye position signal sampled at a time temporally distant from the saccade, which enables precise localization and space constancy for continuous stimuli.

Saccadic Compression of Rectangle and Kanizsa Figures: Now You See It, Now You Don't

Background Observers misperceive the location of points within a scene as compressed towards the goal of a saccade. However, recent studies suggest that saccadic compression does not occur for discrete elements such as dots when they are perceived as unified objects like a rectangle. Methodology/Principal Findings We investigated the magnitude of horizontal vs. vertical compression for Kanizsa figure (a collection of discrete elements unified into single perceptual objects by illusory contours) and control rectangle figures. Participants were presented with Kanizsa and control figures and had to decide whether the horizontal or vertical length of stimulus was longer using the two-alternative force choice method. Our findings show that large but not small Kanizsa figures are perceived as compressed, that such compression is large in the horizontal dimension and small or nil in the vertical dimension. In contrast to recent findings, we found no saccadic compression for control rectangles. Conclusions Our data suggest that compression of Kanizsa figure has been overestimated in previous research due to methodological artifacts, and highlight the importance of studying perceptual phenomena by multiple methods.

A continuously lit stimulus is perceived to be shorter than a flickering stimulus during a saccade

When subjects made a saccade across a single-flashed dot, a flickering dot or a continuous dot, they perceived a dot, an array (phantom array), or a line (phantom line), respectively. We asked subjects to localize both endpoints of the phantom array or line and calculated the perceived lengths. Based on the findings of Matsumiya and Uchikawa (2001), we predicted that the apparent length of the phantom line would be larger than that of the phantom array. In Experiment 1 of the current study, contrary to the prediction, the phantom line was found to be shorter than the phantom array. In Experiment 2, we investigated whether the function underlying the filled-unfilled space illusion (Lewis, 1912) instead of the function underlying the saccadic compression could explain the results. Subjects were asked to localize both endpoints of a line or an array while keeping their eyes fixated. Although the results of Experiment 2 showed that the perceived length of a line was shorter than that of an array, the function underlying the filled-unfilled illusion could not fully account for the results of Experiment 1. To explain the present results, we proposed a model for the localization process and discussed its validity.

Distinct Functions of the Primate Putamen Direct and Indirect Pathways in Adaptive Outcome-Based Action Selection

Cortico-basal ganglia circuits are critical regulators of reward-based decision making. Reinforcement learning models posit that action reward value is encoded by the firing activity of striatal medium spiny neurons (MSNs) and updated upon changing reinforcement contingencies by dopamine (DA) signaling to these neurons. However, it remains unclear how the anatomically distinct direct and indirect pathways through the basal ganglia are involved in updating action reward value under changing contingencies. MSNs of the direct pathway predominantly express DA D1 receptors and those of the indirect pathway predominantly D2 receptors, so we tested for distinct functions in behavioral adaptation by injecting D1 and D2 receptor antagonists into the putamen of two macaque monkeys performing a free choice task for probabilistic reward. In this task, monkeys turned a handle toward either a left or right target depending on an asymmetrically assigned probability of large reward. Reward probabilities of left and right targets changed after 30–150 trials, so the monkeys were required to learn the higher-value target choice based on action–outcome history. In the control condition, the monkeys showed stable selection of the higher-value target (that more likely to yield large reward) and kept choosing the higher-value target regardless of less frequent small reward outcomes. The monkeys also made flexible changes of selection away from the high-value target when two or three small reward outcomes occurred randomly in succession. DA D1 antagonist injection significantly increased the probability of the monkey switching to the alternate target in response to successive small reward outcomes. Conversely, D2 antagonist injection significantly decreased the switching probability. These results suggest distinct functions of D1 and D2 receptor-mediated signaling processes in action selection based on action–outcome history, with D1 receptor-mediated signaling promoting the stable choice of higher-value targets and D2 receptor-mediated signaling promoting a switch in action away from small reward outcomes. Therefore, direct and indirect pathways appear to have complementary functions in maintaining optimal goal-directed action selection and updating action value, which are dependent on D1 and D2 DA receptor signaling.

Development of a system to measure visual functions of the brain for assessment of entertainment

The unique event related brain potential (ERP) called the eye fixation related potential (EFRP) is obtained with averaging EEGs at terminations of saccadic eye movements. Firstly, authors reviewed some studies on EFRP in games and in ergonomics and, secondly introduced a new system for assessment of visual entertainments by using EFRP. The distinctive feature of the system is that we can measure the ERP under the conditions where a subject moves eyes. This system can analyze EEG data from many sites on the head and can display in real time the topographical maps related to the brain activities. EFRP is classified into several components at latent periods. We developed a new system to display topographical maps at three latent regions in order to analyze in more detail psychological and neural activities in the brain. This system will be useful for assessment of the visual entertainment.

Spatiotemporal characteristics of gaze of children with autism spectrum disorders while looking at classroom scenes

Children with autism spectrum disorders (ASD) who have neurodevelopmental impairments in social communication often refuse to go to school because of difficulties in learning in class. The exact cause of maladaptation to school in such children is unknown. We hypothesized that these children have difficulty in paying attention to objects at which teachers are pointing. We performed gaze behavior analysis of children with ASD to understand their difficulties in the classroom. The subjects were 26 children with ASD (19 boys and 7 girls; mean age, 8.6 years) and 27 age-matched children with typical development (TD) (14 boys and 13 girls; mean age, 8.2 years). We measured eye movements of the children while they performed free viewing of two movies depicting actual classes: a Japanese class in which a teacher pointed at cartoon characters and an arithmetic class in which the teacher pointed at geometric figures. In the analysis, we defined the regions of interest (ROIs) as the teacher’s face and finger, the cartoon characters and geometric figures at which the teacher pointed, and the classroom wall that contained no objects. We then compared total gaze time for each ROI between the children with ASD and TD by two-way ANOVA. Children with ASD spent less gaze time on the cartoon characters pointed at by the teacher; they spent more gaze time on the wall in both classroom scenes. We could differentiate children with ASD from those with TD almost perfectly by the proportion of total gaze time that children with ASD spent looking at the wall. These results suggest that children with ASD do not follow the teacher’s instructions in class and persist in gazing at inappropriate visual areas such as walls. Thus, they may have difficulties in understanding content in class, leading to maladaptation to school.

Differential representation of goal in monkey lateral prefrontal cortex in free- and instructed-choice

The prefrontal cortex is credited with contributing to relational reasoning, or the ability to integrate multiple acquired associations to generate new relationships. We have recorded single-unit activity from the lateral prefrontal cortex (LPFC) and the striatum while the monkeys performed a sequential paired-association task with asymmetric reward schedule. In the task, the monkeys learned two sequences of associated stimuli: A1-B1-C1 and A2-B2C2. The asymmetric reward rule was instructed by pairing C1 (or C2) with large (or small) reward block by block. The monkey also learned associations between new stimuli (e.g. N1, N2) and B1 and B2. The new stimuli were presented as the first cue in sequential paired-association trials instead of the old stimuli (A1 and A2). The findings from single-unit activity suggest that the LPFC can use an internal model of category to transfer reward information associated with one stimulus to other stimuli, even to new stimuli that had never been paired with different amount of reward. The striatum only uses direct experience between conditioned stimuli and reward to predict reward. One prediction from this hypothesis is that if the LPFC is inactivated, the monkey still correctly predicts reward for old stimuli through the striatal pathway, but has deficits in predicting reward for new stimuli. We injected muscimol to locally inactivate the LPFC, and also saline into the LPFC as control. In saline sessions, the monkey had significantly higher choice accuracy for new stimuli in large than in small reward trials, but this difference disappeared in muscimol session, consistent with the prediction. Together with single-unit activity data, our results suggest that the LPFC play a critical role in category-based reward inference.