Biology subjects

Postle, B.

Publications and source records attributed to Postle, B..

3 recordsLinked to original sources

bioRxiv2021

The neural mechanisms of active removal from working memory

The ability to frequently update the contents working memory (WM) is vital for the flexible control of behavior. Whether there even exists a mechanism for the active removal of information from working memory, however, remains poorly understood. In this Registered Report we will test the predictions of models for two different (and not mutually exclusive) mechanisms of active removal: adaptation-hijacking and mental-context shifting. We will collect functional magnetic resonance imaging (fMRI) data while subjects perform a novel "ABC-retrocuing" task designed to elicit two modes of removal, active or passive (Shan & Postle, Registered Report). The adaptation-hijacking model posits an adaptation-like modification of perceptual circuits combined with a weak activation of the to-be-removed item. Its predictions will be assessed by using multivariate inverted encoding modeling (IEM) and photic "pings" to assay the state of feature-selective encoding channels and of activity-silent representations under active-removal versus passive-removal conditions. A second model - "working memory episodic memory" (WMEM) - posits that interference from no-longer-relevant information is minimized by making the mental context associated with new information dissimilar from that associated with the to-be-"removed" information. This will be tested by using representational similarity analysis (RSA) to compare the rate of contextual drift under active-removal versus passive-removal conditions.

neuroscience↗

bioRxiv2018

The Role of Location-Context Binding in Nonspatial Visual Working Memory

Successful retrieval of an item from visual working memory (VWM) often requires an associated representation of the trial-unique context in which that item was presented. We dissociated the effects on fMRI signal of memory load versus context binding by comparing nonspatial VWM for one oriented bar vs. three bars individuated by their location on the screen vs. three items drawn from different categories (orientation, color, and luminance), for which location context was superfluous. Delay-period fMRI signal in frontal and parietal cortex was sensitive to stimulus homogeneity rather than to memory load per se. Behavioral performance revealed a broad range in swap errors, an index of the efficacy of context binding, and subjects were classified as high swap error or low swap error. During the delay period, the strength of the representation of stimulus location in parietal cortex predicted individual differences in swap errors. During recall, activity in occipital cortex revealed two dissociable neural correlates of context binding: high swap-error subjects allocated less spatial attention to the location of the probed item and more spatial attention the location of non-probed items; high swap-error subjects also represented the orientation of the probed item more weakly and the orientation of nonprobed items more strongly. Our results suggest context binding is a computation that influences all stages of VWM processing.\n\nSignificance StatementAlthough we often think of the contents of visual working memory (VWM) as representations of the items that need to be remembered, each items trial-unique context is also critical for successful performance. For example, if one observes a red, then a black, then a blue car passing through an intersection, vivid memory for the colors, alone, wouldnt allow one to execute the instruction \"Follow the first of the three cars that just drove by.\" Although manipulating load is commonly assumed to isolate storage functions, requiring memory for multiple items drawn from the same category also increases demands on the context binding needed to individuate these items. This experiment tracked the influence of context binding on VWM stimulus processing.

neuroscience↗

bioRxiv2016

Prestimulus alpha-band power biases visual discrimination confidence, but not accuracy

Oscillations in the alpha-band (8-13 Hz) of human electroencephalographic (EEG) recordings are thought to reflect cortical excitability. As such, the magnitude of alpha power prior to the onset of a near threshold visual stimulus has been shown to predict stimulus detectability. Mechanistically, however, non-specific increases in visual-cortical excitability should result in amplified signal as well as amplified noise, leaving actual discriminability unchanged. Using a two-choice orientation discrimination task with equally probable stimuli, we found that discrimination accuracy was unaffected by fluctuations in prestimulus alpha-band power. Decision confidence, on the other hand, was strongly negatively correlated with prestimulus alpha power. This finding constitutes a clear dissociation between objective and subjective measures of visual perception as a function of prestimulus cortical excitability. This dissociation is predicted by models of perceptual confidence under which the balance of evidence in favor of each choice drives objective performance but only the magnitude of evidence in favor of the chosen stimulus drives subjective reports, suggesting that human perceptual confidence can be suboptimal.

neuroscience↗