Separate visual representations for perception and for visually guided behavior

Converging evidence from several sources indicates that two distinct representations of visual space mediate perception and visually guided behavior, respectively. The two maps of visual space follow different rules; spatial values in either one can be biased without affecting the other. Ordinarily the two maps give equivalent responses because both are veridically in register with the world; special techniques are required to pull them apart. One such technique is saccadic suppression: small target displacements during saccadic eye movements are not preceived, though the displacements can change eye movements or pointing to the target. A second way to separate cognitive and motor-oriented maps is with induced motion: a slowly moving frame will make a fixed target appear to drift in the opposite direction, while motor behavior toward the target is unchanged. The same result occurs with stroboscopic induced motion, where the frame jump abruptly and the target seems to jump in the opposite direction. A third method of separating cognitive and motor maps, requiring no motion of target, background or eye, is the Roelofs effect: a target surrounded by an off-center rectangular frame will appear to be off-center in the direction opposite the frame. Again the effect influences perception, but in half of the subjects it does not influence pointing to the target. This experience also reveals more characteristics of the maps and their interactions with one another, the motor map apparently has little or no memory, and must be fed from the biased cognitive map if an enforced delay occurs between stimulus presentation and motor response. In designing spatial displays, the results mean that what you see isn't necessarily what you get. Displays must be designed with either perception or visually guided behavior in mind

[Activities of Psychology Dept., California Univ.]

We have completed two studies during the grant period, with manuscripts published or ready for submission for publication: (1) Dual adaptation and adaptive generalization in the human vestibuloocular reflex and (2) Frequency vs. acceleration specificity in human VOR adaptation. In the 1st study two studies examined the possibility that rotational VOR plasticity is subject to dual adaptation and adaptive generalization. Subjects in the experimental condition were exposed to an altered visual-vestibular environment for about four minutes every day for five consecutive days. The working hours between these testing sessions constituted re-exposure to the normal visual environment. Thus, subjects were repeatedly adapting and re-adapting to both environments which is a condition designed to produce dual adaptation. In each training session a measure of baseline VOR gain was obtained (in the dark). A small laser spot (the only visual stimulus) was systematically moved in the same direction as the subject's head, but by half the angle of rotation (target/head gain = 0.5). This resulted in adaptation values relativized to the non-adapted gain of each subject. These values were then analyzed using an analysis of variance with day and session (within a day) as factors. In the 2nd study human VOR adaption has been assumed to be frequency specific, despite the fact that the semicircular canals are simulated by rotational acceleration and not frequency per se

Microsaccades and Visual-Spatial Working Memory

Observers performed working memory tasks at varying retinal eccentricities, fixating centrally while microsaccade rates and directions were monitored. We show that microsaccades generate no interference in a working memory task, indicating that spatial working memory is at least partially insulated from oculomotor activity. Intervening tasks during the memory interval affected memory as well as microsaccade patterns. Average microsaccade rate peaks after appearance of a fixation cross at the start of a trial, and dips at cue onset and offset. Direction of stimuli in choice tasks did not influence micro-saccade direction, however. Poorer memory accuracy for locations at greater retinal eccentricity calls for revising ideas of short-term spatial representations to include retinotopic or allocentric code

Visual vs. Spatial Contributions to Microsaccades and Visual-Spatial Working Memory

Microsaccade rates and directions were monitored while observers performed a visual working memory task at varying retinal eccentricities. We show that microsaccades generate no interference in a working memory task, indicating that spatial working memory is at least partially insulated from oculomotor activity. Intervening tasks during the memory interval affected microsaccade patterns; microsaccade frequency was consistently higher during concurrent spatial tapping (no visual component) than during exposure to dynamic visual noise (no task). Average microsaccade rate peaked after appearance of a fixation cross at the start of a trial, and dipped at cue onset and offset, consistent with previous results. Direction of stimuli in choice tasks did not influence microsaccade direction,however

Microsaccades and Exploratory Saccades in a Naturalistic Environment

Microsaccades, small saccadic eye movements made during fixation, might accompany shifts of visual attention, serve to refresh the retinal image, or have some other function. We tested the relative importance of these functions by recording exploratory saccades and microsaccades with a free head during a lane-change task in a simulated driving environment, accompanied by a simultaneous visual search task in which drivers searched for a target among similar distractors on a panel to the driver's right where an electronic display would normally be located. After training, observers performed a baseline run with the lane-change task only, followed by four dual-task runs and a final control run. In the dual-task condition, where more visual attention shifts occur, we found a significantly increased frequency of microsaccades along with an even larger increase in frequency of large exploratory saccades. However the proportion of microsaccades significantly decreased in the dual task, consistent with the idea of a common neurological origin for microsaccades and exploratory saccades

Dual Adaptation and Adaptive Generalization of the Human Vestibulo-Ocular Reflex

In two experiments, we examined the possibility that the human vestibulo-ocular reflex (VOR) is subject to dual adaptation (the ability to adapt to a sensory rearrangement more rapidly and/or more completely after repeated experience with it) and adaptive generalization (the ability to adapt more readily to a novel sensory rearrangement as a result of prior dual adaptation training). In Experiment 1, the subjects actively turned the head during alternating exposure to a visual-vestibular rearrangement (target/head gain = 0.5) and the normal situation (target/head gain = 0.0). These conditions produced both adaptation and dual adaptation of the VOR but no evidence of adaptive generalization when tested with a target/head gain of 1.0. Experiment 2, in which exposure to the 0.5 gain entailed externally controlled (i.e., passive) whole body rotation, resulted in VOR adaptation but no dual adaptation. As in Experiment 1, no evidence of adaptive generalization was found

Space-independent modality-driven attentional capture in auditory, tactile and visual systems

Abstract Extending previous evidence for attentional shifts across auditory and visual modalities without the confound of the two modalities originating at different location

The Computational Brain.

Keywords: reductionism, neural networks, distributed coding, Karl Pribram, computational neuroscience, receptive field 1.1 The broad goal of this book, expressed at the start, is ``to understand how neurons give rise to a mental life.'' A mental reductionism is assumed in this seductively simple formulation. Indeed, the book represents reductionism at its best, as the authors guide the reader through the many intermediate levels that link neurons with mental life. In so doing they attack a problem that has persisted for some decades in the neurosciences, since the development of single-cell recording methods. The problem is that millions of neurons participate in every behaviorally meaningful activity, but we normally record from only one neuron at a time, or at best a handful. The temptation is great to overestimate the one-millionth sample obtained from a single neuron, to interpret its activity as detecting a perceptual situation or driving a motor response. This approach, seemingly inescapable in the 1960s, became untenable, but there were no concrete alternatives. Evoked potential techniques gave only a gross average of activity, too vague to pin down mechanisms, and early PDP (parallel distributed processing, or artificial neural network) models were too biologically unrealistic to provide viable interpretations of the single-cell data. Churchland and Sejnowski show how distributed models can now attack this problem, providing significant insights into brain function in a number of domains. 1.2 The book has several parts. First, the authors introduce their approach, combining anatomical, physiological, behavioral and modelling methods in an integrated interdisciplinary attack on specific functional systems. There follows a review of enough anatomy and neurophysiology to make the authors' viewpoint clear and to provide a background for integrating PDP modelling into specific problems in the neurosciences. The heart of the book is a series of chapters reviewing particular models that have been successful in increasing our understanding of the functioning of biological brains. Models of reflex reactions in invertebrates, of locomotion, the vestibulo-ocular reflex in primates