Contrast sensitivity revealed by spontaneous eyeblinks: Evidence for a common mechanism of oculomotor inhibition.

Spontaneous eyeblinks are known to serve important physiological functions, and recent evidence shows that they are also linked to cognitive processes. It is yet unclear whether this link reflects a crude rate modulation or, alternatively, an automatic and precise process, tightly linked to the low-level properties of sensory stimuli. We have recently reported (Y. S. Bonneh, Adini, & Polat, 2015) that, for microsaccades, the onset and release from inhibition in response to transient stimuli depend systematically on the low-level stimulus parameters. Here we reanalyzed our previous data for both microsaccades and eyeblinks for observers with sufficient blinking (>10% of trials, 18 of 23 observers tested) who watched and silently counted sequences of Gabor patches at 1 Hz with varied contrast and spatial frequency. We found that spontaneous eyeblinks, although less frequent, were similar to microsaccades in their modulation pattern in response to transient stimuli, demonstrating inhibition and rebound, which were dependent on the contrast and spatial frequency of the stimuli. The average blink response time, measured as the latency of the first blink following its release from inhibition, was longer for lower contrast and higher spatial frequency. Importantly, it was highly correlated with a similar measure for microsaccades as well as with psychophysical measures of contrast sensitivity. These results suggest that both eyeblinks and microsaccades are linked to the same inhibitory mechanism that presumably turns off oculomotor events while processing previous events and generates a rebound effect upon its release. The onset of both eyeblinks and microsaccades may thus reflect the time course of this mechanism and the associated cognitive process.