The Effect of Blinks and Saccadic Eye Movements on Visual Reaction Times

By Johns, Murray; Crowley, Kate et al. | Attention, Perception and Psychophysics, May 2009 | Go to article overview

The Effect of Blinks and Saccadic Eye Movements on Visual Reaction Times


Johns, Murray, Crowley, Kate, Chapman, Robert, Tucker, Andrew, Hocking, Christopher, Attention, Perception and Psychophysics


Vision is suppressed during blinks and saccadic eye movements. We hypothesized that visual reaction times (RTs) in a vigilance test would be significantly increased when a blink or a saccade happened to coincide with the stimulus onset. Thirty healthy volunteers each performed a visual RT test for 15 min while their eye and eyelid movements were monitored by a system of infrared reflectance oculography. RTs increased significantly, many by more than 200 msec, when a blink occurred between 75 msec before and up to 150 msec after the stimulus onset. A similar result was observed with saccades that started 75 to 150 msec after the stimulus. Vision or attention was evidently inhibited before each blink and for longer than the saccades lasted. We suggest that visual suppression is involved in this process, which could explain some of the normal variability in RTs over periods of seconds that has not been adequately explained before.

Every time we blink, voluntarily or involuntarily, we cannot see, for two reasons: The upper eyelids cover the pupils and prevent most light from reaching the retina, and vision is suppressed centrally by a process called blink suppression (Volkmann, Riggs, & Moore, 1980). This has been demonstrated by experiments that have bypassed the pupils, sending light to the retina via the roof of the mouth, which has shown that visual suppression still occurs during blinks (Volkmann et al., 1980). Functional MRI under those circumstances has indicated reduced neuronal activity that is specific to the visual system, which could account for the reduced sensitivity to light. There is also reduced activity in the parietal and prefrontal cortex, however, which suggests more general inhibition of awareness during blinks (Bristow, Haynes, Sylvester, Frith, & Rees, 2005; Burr, 2005). Blink suppression begins before the start of each blink and ends after it finishes, lasting about 200-250 msec (Volkmann et al., 1980).

A similar process, called saccadic suppression, prevents us from being aware of the blurred images that would otherwise occur during rapid eye movements such as saccades, which we make as we look from one point to another (Volkmann, Schick, & Riggs, 1968). Saccadic suppression is mainly central in origin, but it has an additional retinal component of control (Diamond, Ross, & Morrone, 2000). Saccadic suppression begins before the start of the saccade and ends after it, lasting about 100-150 msec (Volkmann et al., 1968). Blink and saccadic suppression share some mechanisms, but they are not identical (Ridder & Tomlinson, 1997). Given that we usually blink about 15-20 times per min (Leigh & Zee, 2006), involving perhaps 4 sec of visual suppression, and that we have about 40 or more saccades per min, involving another 4 or 5 sec of suppression, it is surprising that we are not aware of being functionally blind for 10%-15% of the time under normal circumstances. Our visual awareness is evidently extrapolated across periods that are "missing." The implications of this for psychomotor performance, as measured by visual reaction times and vision in daily life, have not been well canvassed.

Reaction time (RT)-how quickly someone responds to a visual stimulus that is presented repeatedly at random intervals- has long been used to measure psychomotor performance and brain function (Donders, 1868/1969; Luce, 1986). For example, many current theories of visual attention are based on changes in RT performance (Eriksen & Eriksen, 1974; Posner, Snyder, & Davidson, 1980). The resulting mean RT, RT variance, and response accuracy have often been used to infer "attention" or "distraction" effects (Van Breukelen et al., 1995). As part of our ongoing investigations into the variability of RTs, we wanted to know whether the visual suppression that is known to accompany blinks and saccades influences individual RTs under normal circumstances. Our hypothesis was that when the start of a stimulus happens to coincide with a blink or a saccade, that RT will be increased, because the stimulus will not be perceived until after the visual suppression has ended. …

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