How regularities shape visual perception: aesthetic preferences, form discrimination, and geometric hallucinations

The human visual system efficiently processes complex visual information by integrating regularities across space and time, such as symmetry, geometrical form, and temporal frequency, to ultimately create coherent percepts. However, open questions remain about how the visual system encodes such regularities and at which stages along its processing hierarchy they are integrated. This thesis illustrates three visual perception studies: one exploring the role of context-based symmetry in aesthetic preference, and the remaining two investigating the spatial and temporal dynamics underlying form perception, with a focus on veridical and illusory geometric patterns respectively. In the first study, the role of bilateral symmetry on aesthetic judgments was examined across various stimuli, including abstract shapes, landscapes, flowers, and human faces. These images were shown to viewers, asking them to provide explicit aesthetic ratings and engage in an Implicit Association Test (IAT) to collect implicit behavioral measures. Interestingly, implicit measures demonstrated indiscriminate positive associations between symmetry and goodness across image categories of interest, whereas explicit measures showed a more nuanced pattern with respect to the aesthetic impact of symmetry in the same categories. These findings suggest a dissociation between implicit and explicit measures of human appreciation for symmetry when this feature is embedded in different types of objects and scenes. The second study investigated form and motion integration using Glass patterns (GPs), a class of visual stimuli in which global structure emerges from locally oriented dot pairs. Static GPs consist of a single-frame ensemble of dot pairs arranged in a fixed configuration, whereas dynamic GPs are built through the close temporal juxtaposition of frames displaying different configurations. By manipulating the number of unique frames and the pattern update rate, we investigated the impact of these two factors on discrimination thresholds for circular, radial, and spiral dynamic GPs. Results replicated previous findings that circular GPs are more easily perceived than radial and spiral GPs, exhibiting lower discrimination thresholds. Additionally, discrimination thresholds decreased with an increasing number of unique frames, while the effect of the pattern update rate was negligible. These findings hint at a mechanism of summation of form signals sampled from unique frames, but do not clearly support temporal integration based on the update rate. In the third study, the effects of flicker frequency and rhythmicity on geometric form perception were explored using flicker light stimulation. Participants were exposed to four different types of luminance flicker, resulting from the combination of two levels of frequency with two levels of rhythmicity. Electroencephalography (EEG) was used to record neural responses to flicker light stimulation. Participants were asked to categorize ambiguous static GPs featuring a mixture of radially- and spirally-oriented dot pairs. Behavioral data revealed that the probability of categorizing a pattern as radial or spiral varied with flicker frequency, with a stronger and temporally accruing bias observed under rhythmic flicker conditions. Overall, these experiments demonstrate how complex interactions of spatial and temporal regularities in visual input can affect human vision at different levels, influencing both perceptual decision- making and aesthetic judgments. The findings contribute to a broader understanding of how visual perception mechanisms rely on regularity to make sense of the world around us.