Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Is the early modulation of brain activity by fearful facial expressions primarily mediated by coarse low spatial frequency information

Abstract: Rapidly decoding the emotional content of a face is an important skill for successful social behavior. Several Event Related brain Potential (ERP) have indicated that emotional expressions already influence brain activity as early as 100 ms. Some studies hypothesized that this early brain response to fear depends on coarse-magnocellular inputs, which are primarily driven by Low Spatial Frequency (LSF) cues. Until now however, evidence is inconclusive probably due to the divergent methods used to match luminance and contrast across spatial frequencies and emotional stimuli. In the present study, we measured ERPs to LSF and HSF faces with fearful or neutral expressions when contrast and luminance was matched across SF or not. Our findings clearly show that fearful facial expressions increases the amplitude of P1 (only for contrast–luminance equated images) and N170 in comparison to neutral faces but only in LSF faces, irrespective of contrast or luminance equalization, further suggesting that LSF information plays a crucial role in the early brain responses to fear. Furthermore, we found that, irrespective of luminance or contrast equalization, N170 occurred faster faster when perceiving LSF faces than HSF faces, again emphasizing the primacy of LSF processing in early face perception.

Early binding of feature pairs for visual perception.

Abstract: If features such as color and orientation are processed separately by the brain at early stages1,2, how does the brain subsequently match the correct color and orientation? We found that spatially superposed pairings of orientation with either color or luminance could be reported even for extremely high rates of presentation, which suggests that these features are coded in combination explicitly by early stages, thus eliminating the need for any subsequent binding of information. In contrast, reporting the pairing of spatially separated features required rates an order of magnitude slower, suggesting that perceiving these pairs requires binding at a slow, attentional stage.

Visual features that vary together over time group together over space

Abstract: The visual system perceives objects as coherent even when some parts are hidden or discontinuous. How this representation is constructed from local features of many nearby objects is termed the 'binding problem.' Here we manipulate contrast in several drifting gratings that can be perceived as either independent objects or parts of a single object. Contrast modulations that are correlated in time enhance perceptual coherence, whereas uncorrelated modulations impair coherence. Presumably, correlated contrast modulations produce correlated responses in cortical neurons. Therefore, our results are consistent with the hypothesis that temporal correlation of neural activity is important for feature binding.