The role of parietal cortex in the formation of color and motion based concepts.

Imaging evidence shows that separate subdivisions of parietal cortex, in and around the intraparietal sulcus (IPS), are engaged when stimuli are grouped according to color and to motion (Zeki and Stutters, 2013). Since grouping is an essential step in the formation of concepts, we wanted to learn whether parietal cortex is also engaged in the formation of concepts according to these two attributes. Using functional magnetic resonance imaging (fMRI), and choosing the recognition of concept-based color or motion stimuli as our paradigm, we found that there was strong concept-related activity in and around the IPS, a region whose homolog in the macaque monkey is known to receive direct but segregated anatomical inputs from V4 and V5.

Masking within and across visual dimensions: psychophysical evidence for perceptual segregation of color and motion.

Visual masking can result from the interference of perceptual signals. According to the principle of functional specialization, interference should be greatest when signal and mask belong to the same visual attribute (e.g.

Subliminal gamma flicker draws attention even in the absence of transition-flash cues.

We recently reported evidence indicating that selective attention is deployed to a target location in a multi-object display, when the target event (a change of one of the objects) is preceded by subliminal flicker in the gamma range. However, concerns have been raised regarding the stimuli used in this study and the possible contribution of an artifactual cue: a "transition flash" between pretarget flicker offset and target onset. Here, we report a series of experiments investigating the existence and potential contribution to selective attention of this transition-flash cue under different presentation conditions.

Gamma flicker triggers attentional selection without awareness.

Gamma band modulations in neural activity have been proposed to mediate attentional processes. To support a causal link between gamma activity and attentional selection, we attempt to evoke gamma oscillations by a 50-Hz subliminal flicker. We find that a subliminal 50-Hz flicker at a target location, before target presentation, speeds up and enhances target detection and discrimination.