Ester, E. F. | Search bioRxiv

bioRxiv2021

Spatial working memory representations in human cortex are robust to a task-irrelevant interrupting stimulus

Visual working memory (WM) enables the maintenance and manipulation of information no longer accessible in the visual world. Previous research has identified spatial WM representations in activation patterns in visual, parietal, and frontal cortex. In natural vision, the period between the encoding of information into WM and the time when it is used to guide behavior (the delay period) is rarely "empty", as is the case in most of the above laboratory experiments. In naturalistic conditions, eye movements, movement of the individual, and events in the environment result in visual signals which may overwrite or impair the fidelity of WM representations, especially in early sensory cortices. Here, we evaluated the extent to which a brief, irrelevant interrupting visual stimulus presented during a spatial WM delay period impaired behavioral performance and WM representation fidelity assayed using an image reconstruction technique (inverted encoding model). On each trial, participants (both sexes) viewed two target dots and were immediately post-cued to remember the precise spatial position of one dot. On 50% of trials, a brief interrupter stimulus appeared. While we observed strong transient univariate visual responses to the distracter stimulus, we saw no change in reconstructed neural WM representations under distraction, nor a change in behavioral performance on a continuous recall task. This suggests that spatial WM representations may be particularly robust to interference from incoming task-irrelevant visual information, perhaps related to their role in guiding movements.

neuroscience↗

bioRxiv2017

Category learning biases sensory representations in visual cortex.

Categorization allows organisms to generalize existing knowledge to novel stimuli and to discriminate between physically similar yet conceptually different stimuli. Humans, nonhuman primates, and rodents can readily learn arbitrary categories defined by low-level visual features, and learning distorts perceptual sensitivity for category-defining features such that differences between physically similar yet categorically distinct exemplars are enhanced while differences between equally similar but categorically identical stimuli are reduced. We report a basis for these distortions in human occipitoparietal cortex. In three experiments, we used an inverted encoding model to recover population-level representations of stimuli from multivoxel and multi-electrode patterns of human brain activity while human participants (both sexes) classified continuous stimulus sets into discrete groups. In each experiment, reconstructed representations of to-be-categorized stimuli were systematically biased towards the center of the appropriate category. These biases were largest for exemplars near a category boundary, predicted participants overt category judgments, emerged shortly after stimulus onset, and could not be explained by mechanisms of response selection or motor preparation. Collectively, our findings suggest that category learning can influence processing at the earliest stages of cortical visual processing. Significance StatementCategory learning enhances perceptual sensitivity for physically similar yet categorically different stimuli. We report a possible mechanism for these distortions in human occipitoparietal cortex.. In three experiments, we used an inverted encoding model to recover population-level representations of stimuli from multivariate patterns in occipitoparietal cortex while participants categorized sets of continuous stimuli into discrete groups. The recovered representations were systematically biased by category membership, with larger biases for exemplars adjacent to a category boundary. These results suggest that mechanisms of categorization shape information processing at the earliest stages of the visual system.

neuroscience↗