Abstract
[Goal] Recent studies have reported that alpha band (8-12 Hz) entrainment by periodic visual flashes can cause performance oscillations in hit rate or reaction time over several cycles. Here, we investigated whether a single flash is sufficient to trigger oscillations in discriminability over time.
[Methods] Observers performed a 2AFC orientation discrimination task on Gabor patches. We titrated individual orientation discrimination thresholds at 79% accuracy for each visual hemifield. Gabor patches were presented in both hemifields for 50 ms following 15 unilateral flashes within the alpha band frequency range (Experiment 1) or a single unilateral flash (Experiment 2), with delays ranging from 100 to 250 ms in 16.7 ms steps. Shortly after stimulus offset, a response cue indicated the target Gabor.
[Results] In Experiment 1, most observers showed significant unilateral or bilateral visual discriminability (d’) oscillations, after entraining either the left or the right hemifield. Remarkably, in Experiment 2, most observers also showed significant unilateral or bilateral d’ oscillations when either hemifield was stimulated with just a single flash. In both experiments, the oscillation amplitudes were similar and the d’ oscillations ranged from 8 to 29 Hz in frequency.
[Conclusions] These novel results show that visual discriminability oscillates following either a single visual flash or alpha band periodic flashes. The onset of a flash is likely to phase-reset neural oscillations and elicit d’ oscillations. These results indicate that entrainment with periodic flashes is not necessary for performance oscillations, and suggest that internally-driven rhythms, encompassing alpha band and beyond, modulate visual discrimination sensitivity.