Academic journal article Attention, Perception and Psychophysics

News from the Field

Academic journal article Attention, Perception and Psychophysics

News from the Field

Article excerpt

Published online: 25 June 2014

© The Psychonomic Society, Inc. 2014

SUMMARY STATISTICS

Weighting for the end

Cheadle, S., Wyart V., Tsetsos, K., Myers, N., de Gardelle, V., Herce Castañón., S., & Summerfield, C. (2014). Adaptive gain control during human perceptual choice. Neuron, 81(6), 1429-1441

The dynamics of many neural systems are now well known. For example, Bloch'slawtellsusthatthere must be light-sensitive neurones somewhere near the front-end of the visual system capable of integrating luminance over short periods of time with nearly con- stant efficiency. When stimulation lasts a long time, those neurones adapt, and their responses are attenuated accordingly. By definition, such adaptation qualifies as gain control.

In a heretofore unrelated literature, many scientists have begun studying tasks that require observers to form summary statistics of perceptual stimuli. These tasks have become popular because they offer a way to gauge the efficiencies of cognitive or decision pro- cesses, for which hard-wired neural mechanisms are unlikelytoexist.

Various subsets of Cheadle's co-authors have previously written about a special kind of summary statistic, and in their latest paper they examine the dynamics of its computation from psychophysical and physiological perspectives. Their findings suggest adaptation beyond the level of stimulus encoding: gain control seems to operate at the level of infor- mation integration too.

The task is to decide whether a serial presentation of Gabor elements is-on average-closer to the cardinal axes (i.e. +) or the inter-cardinal axes (i.e. ×). Unlike most of the other statistics currently under scrutiny, this one has the advantage that the (signed) diagnosticity of any two elements becomes more similar as their physical difference increases. For example a vertical Gabor supports the cardinal decision just as much as a horizontal one.

The largest effect recorded by Cheadle et al. is that later Gabors in the series had more impact on decisions and pupil diameter than earlier Gabors had. More interesting is their finding that the impact of an individual Gabor, not only on decision and pupil size but certain BOLD and EEG signals too, varied inversely with the difference between its diagnosticity and that of the preceding Gabor. For example, a vertical Gabor following a horizontal Gabor would contrib- ute more to decisional processes than a vertical Gabor follow- ing any tilted Gabor.

Perhaps this study's most important contribution is the model it proposes for the dynamics of information integration, in which both of these effects ("recency" and "consistency") are natural by-products. Quite simply, it's gain control for diagnosticity. We seem to adjust ourselves for maximum sensitivity to incoming evidence that confirms our expecta- tions. Initial impressions and surprises are consequently down-weighted.

Cheadle et al. did not vary the rate of presentation, so we do not yet know how long it takes for the gain-control process to kick in. Is there a Bloch-like epoch, in which all diagnosticity is equally weighted? Only (systematically varying display) time will tell.-J.A.S.

VISUALWORKING MEMORY

Models of response times

Donkin, C., Nosofsky, R. M., Gold, J. M., & Shiffrin, R. M. (2013). Discrete-slots models of visual working-memory re- sponse times. Psychological Review, 120,873-902.

The nature of visual working memory (i.e., discrete slots or continuous resource) has been a matter of debate, mainly based on accuracy data from various tasks. The discrete-slot view assumes that VWM consists of a limited number of slots with fixed resolution, whereas the continuous-resource view assumes that VWM can be divided among all the items, with flexible resolution. Recently, Donkin, Nosofsky, Gold, and Shiffrin (2013) attempted to open new windows on this debate by examining response time data in a visual change-detection task of colors. …

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