Expectations Change the Temporal Discrimination of Flashing Stimuli

The temporal sensitivity of human visual system was investigated. The two separate lights flashing at different temporal intervals were presented under neutral background. The three primary LED's (red, green and blue) were used as flash lights. The background extending full visual field was illuminated by D65 illuminant composed of three primary LED's. As each pair of stimuli flashed, subject reported "same", different", "left-first", or "right-first" to indicate whether the two lights appeared to flash at the same or at different times. We previously found that the temporal discrimination process has three stages (Stanikunas et al, 2012, Perception, 41 ECVP Supplement, 89). At the first stage stimuli are perceived as flashing together. At the second stage flashes are perceived as different in time, but it is not possible to tell which stimulus flashes first. At the third stage it is clearly visible which stimulus flashed first. Here we investigate how advanced knowing of stimulus flash order and expectations affect temporal sensitivity. Knowing. The threshold for temporal discrimination was measured by method of limits. Before each experiment subject either were instructed which stimulus will flash first, or didn't know flash order. Results show that knowing of stimulus flash order increases sensitivity for temporal discrimination and reduces decision errors. When the flash order is not known, perceptual errors are made during period of uncertainty. Expectation. Before each flash subjects were instructed to expect that stimuli will flash "left-first", "right-first" or will flash together. All stimulus timing presentation and three expectation instructions were presented in pseudo random order. We find that temporal discrimination threshold is affected by expectation. Lowest thresholds are when expectation coincides with flash presentation and biggest thresholds are when expecting opposite stimulus presentation. Meeting abstract presented at VSS 2014