Moharramipour, A. | Search bioRxiv

bioRxiv2024

Representation of visual uniformity in the lateral prefrontal cortex

Visual illusions tend to have early visual cortical correlates. However, this general trend may not apply to our subjective impression of a detailed and uniform visual world, which may be considered illusory given the paucity of peripheral processing. Using a psychophysically calibrated visual illusion, we assessed the patterns of hemodynamic activity in the human brain that distinguished between the illusory percept of uniformity in the periphery (i.e., Gabor patches having identical orientations) from the accurate perception of incoherence. We identified voxel patterns in the lateral prefrontal cortex that predicted perceived uniformity, which could also generalize to scene uniformity in naturalistic movies. Because similar representations of visual uniformity can also be found in the intermediate and late layers of a feedforward convolutional neural network, the perception of uniformity may involve high-level coding of abstract properties of the entire scene as a whole, that is distinct from the filling-in of specific details in early visual areas.

neuroscience↗

bioRxiv2024

Is subjective perceptual similarity metacognitive?

Perceptual similarity is a cornerstone for human learning and generalization. However, in assessing perceptual similarity between two stimuli, it is not well-defined which features or combinations of features one should focus on. The problem has accordingly been considered ill-posed, implying a lack of a clear ground-truth basis for similarity judgments. We hypothesized that the stimuli rated as subjectively similar are those that are, in fact, more challenging for oneself to discern in practice, in near-threshold settings (e.g., psychophysics experiments). Therefore, an individuals perceptual discrimination capacities can serve as a quasi-objective ground truth for determining whether two stimuli should be judged as similar. To test this idea, we asked participants to rank the similarity of face pairs and also separately measured their discrimination capacity for those pairs. We found a positive association between perceptual discrimination capacity and subjective perceptual dissimilarity, with this association being specific to each individual. The results indicate that perceptual similarity judgments reflect and predict ones own perceptual discrimination capacities. Overall, although subjective, similarity judgments are normative in that they are grounded in ones perceptual capacities, which can be measured through a psychophysical task with objective responses.

neuroscience↗