student profile: Ms Huihui Zhang Zhang


Thesis work

Thesis title: Behavioural oscillations of sensitivity and criterion synchronised with action

Supervisors: David ALAIS , Alexander HOLCOMBE

Thesis abstract:

Previous studies have shown that voluntary action can synchronize brain oscillations, resulting in rhythmical fluctuation of visual contrast sensitivity. In this study, we examined whether voluntary action could synchronize oscillations of decision criterion as well as sensitivity. Participants voluntarily pressed a button to start each trial. After variable times (0 - 800 ms, sampled every 5 ms), a brief grating embedded in noise was presented at the fovea and participants discriminated its orientation (45° or -45°). Using signal detection theory, we calculated participants’ sensitivity and criterion over time. To test the existence of oscillations, we fitted first-order Fourier series to the time series of sensitivity and criterion. We also performed Fast Fourier Transforms on these time series. With the permutation test, we found alpha oscillations of both sensitivity and criterion synchronized with voluntary action, but at different frequencies: 8.5 Hz for sensitivity and 10.4 Hz for criterion. To further reveal whether the oscillation of criterion is due to the oscillation of perceptual bias or motor bias, we recruited another group of participants. They did the same task, except that the mapping between mouse responses (left or right) and the grating orientations was reversed. When combining data from both groups of participants, we found that the sensitivity oscillated at 8.4 Hz, and that the motor bias rather than perceptual bias oscillated at 10.3 Hz. Our findings may suggest different roles of alpha oscillations: alpha oscillations of sensitivity reflect rhythmic attentional inhibition, whereas alpha oscillations of criterion indicate the dynamic motor preparation.

Note: This profile is for a student at the University of Sydney. Views presented here are not necessarily those of the University.