Correlations between Visual Temporal Resolution and Individual Alpha Peak Frequency: Evidence that Internal and Measurement Noise Drive Null Findings.

Abstract

The brain organizes the continuous flow of sensory input by parsing it into discrete events. In the case of 2 flashes separated by a brief ISI, for example, perception may be of a single flash or 2 distinct flashes, depending on the ISI but also on the speed of processing. A number of studies have reported evidence that participants with a higher EEG peak alpha frequency are able to detect the presence of 2 flashes separated by short intervals, whereas those with slower alpha report only 1 flash. Other studies have not found this correlation. We investigated potential factors that might mask the relationship between individual alpha frequency and visual perception. We recorded resting-state EEG from a large sample of participants (n = 50) and measured the temporal resolution of visual perception with the 2-flash fusion task. We found that individual alpha frequency over posterior channels predicted the 2-flash fusion threshold, in line with previous studies, but this correlation was significant only when taking into account the steepness of the psychophysical curve of the 2-flash task. Participants with a relatively shallow psychophysical curve, likely reflecting high sensory and/or decision noise, failed to show this relationship. These findings replicate previous reports of a correlation between alpha frequency and visual temporal resolution, while also suggesting that an explanation of two-flash fusion performance that neglects the role of internal noise might be insufficient to account for all individual differences.