ИСТИНА

Introduction. Large amount of data suggest that various characteristics of visual stimuli are processed by the ventral part of the visual cortex. Although the areas of the brain responsible for the perception of complex objects such as faces are fairly well established, it was more difficult to localize cortex areas that process simpler visual characteristics such as the color and shape of objects. For example, there is conflicting data on the role of the hV4 area (human V4) in visual perception: some studies have found that this area is involved exclusively in the processing of color information (Bannert & Bartels, 2018) or other characteristics of stimuli (Seymour et al., 2010). Other studies show that the color and shape information is processed in other areas of the ventral visual cortex (Wade et al., 2002). We suggest that the reason for this discrepancy is due to the peculiarities of experimental procedures. In most studies, experimental schemes are designed so that subjects perceive stimuli passively, without performing any task. In our opinion, perception is an active process that depends on the task being performed by a person at the moment. In our study, the subjects were given a task in which they were required to select and remember individual characteristics of visual stimuli. The aim of the study is to identify areas of the ventral visual cortex involved in processing the color and shape of stimuli. Methods. The subjects (N = 22, M = 19.6 years, SD = 1.84) were presented with the picture of color blot for 400 ms time period (there were 8 different shapes and 9 colors). The task was to remember either the color or shape, or both characteristics together. In the control series, the same stimuli were presented, but the task was to count the number of figures with a certain color. EEG was recorded (19 channels, 10-20% system) and evoked potentials (ERP) were calculated for presenting an image with a figure in each of the series. Based on the results obtained, the sources of brain activity were localized via Brainstorm (Tadel et al., 2011) using the dSPM algorithm (Dale et al., 2000). For further analysis, we selected 8 areas of the ventral visual cortex: V3v, V4, VO1, and VO2 in both hemispheres. Coordinates of areas boundaries according to Wang et al. (2014) were adapted for Brainstorm. Using the Granger causality estimation method (Seth et al., 2015), causal relationships between these areas of the ventral visual cortex were calculated (see fig. 1). Results and discussion. Both the experimental and control series show activation of VO2 areas in both hemispheres. We assume that the mutual activation of VO2 is associated with the perception of stimuli as already familiar because the experimental design with ERP involves multiple presentation of similar stimuli. In addition, the VO2 area is closely related to the parahippocampal cortex associated with the recognition processes (Aminoff et al., 2013). In the series where color was required to be remembered (both separately and in combination with the form), a strong relationship was found between the V3v and hV4 areas, which we associate with the processing of color information. Finally, in series where the shape of stimuli was required to be remembered, there are strong connections between the VO1 areas of both hemispheres. We propose that these connections is related to the processing of shape information. In addition, in a series in which both color and shape were required to be remembered at the same time, there are bidirectional connections between the hV4 and VO1, which can be associated with the integration of these visual characteristics to form of a holistic image of perception, because the subject's attention is focused not on a single characteristic of the stimulus, but on the stimulus as a whole. Conclusion. Our study clarifies the role of areas of the ventral visual cortex in the perception of color and shape of objects. We suggest that the hV4 area is related with processing color information, the VO1 area is related with processing the shape of objects, and the integration of their activity is related with the formation of a holistic image of perception that combines all the characteristics at once. The research was financially supported by the Russian Science Foundation, project No 19-18-00474