The time of perception and the perception of time are not identical
Often it is assumed that the time of perception is identical or tightly linked to the perception of time. For example, we can clearly perceive a 20 ms delay of two squares presented one after the other at nearby locations (leading to the percept of apparent motion). Thus, it seems reasonable that also conscious perception operates on a "fast" scale. Using a combined feature fusion and TMS experiment, we will show evidence that the duration of conscious perception is rather slow in the range of 300ms to 500ms. During this epoch, stimuli are unconsciously processed. The output of the processing is rendered conscious only at the end of the epoch, even if stimuli were presented for short durations only. We propose that temporal features, such as duration and stimulus onset, are processed and coded as any other feature, such as color and shape, during this epoch. In feature fusion, for example, a red disk is immediately followed by green disk. A yellow disk is perceived. It is impossible to perceive the red and green disk individually, i.e., they are unconscious (Efron, 1967). The same holds true for verniers, which are two vertical lines slightly offset to the left and right. We presented a left offset vernier after a right offset vernier (or vice versa) for 30ms each. Only one single vernier is perceived with a zero offset because the left and right offset integrate unconsciously. We applied TMS at various SOAs, relative to the vernier presentation. Depending on SOA, TMS enhanced selectively, but unconsciously, the contribution of either the first or second vernier to the percept of the single, fused vernier. Surprisingly, even though the verniers were presented for only 60 ms all together, TMS increased the contribution of the first vernier even when presented 360ms after vernier onset. Hence, feature integration and conscious perception cannot be completed beforehand (Scharnowski et al., 2009). We propose that the single vernier is perceived at the end of the 300-500 ms epoch as a "60 ms vernier", as the vernier is perceived as white and aligned. Its duration is coded and rendered conscious as any other feature.
Record created on 2014-12-17, modified on 2016-08-09