Behavioral Evaluation of Movement Cancellation

Abstract

. The countermanding saccade task has been used in many studies to investigate the neural mechanisms that underlie the decision to execute or restrain rapid eye movements. In this task, the presentation of a saccade target is sometimes followed by the appearance of a stop cue that indicates that the subject should cancel the planned movement. Performance has been modeled as a race between motor preparation and cancellation processes. The signal that reaches its activation threshold first determines whether a saccade is generated or cancelled. In these studies, an important parameter is the time required to process the stop cue, referred to as the stop signal reaction time (SSRT). The SSRT is estimated using statistical approaches, the validity of which has not been unequivocally established. A more direct measure of this parameter might be obtainable if a method was available to "unmask" the developing motor command. This can be accomplished by air-puffevoked blinks, which inhibit pontine omnipause neurons that serve as an inhibitory gate for the saccadic system. In the present study, brief puffs of air were used to elicit blinks at various times while rhesus monkeys performed a countermanding saccade task. If the developing motor command has not yet been cancelled, this should trigger a saccade. When blinks occurred between ϳ50 and 200 ms after target onset, saccades were often evoked. Saccades were rarely evoked more than ϳ70 ms after stop cue onset; this value represents a behavioral evaluation of SSRT and was comparable to the estimates obtained using standard statistical approaches. When saccades occurred near the SSRT on blink trials, they were often hypometric. Furthermore, Monte Carlo simulations were performed to model the effects of blink time on the race model. Overall, the study supports the validity of the statistical methods currently in use.

Validation of a within-trial measure of the oculomotor stop process

“…This advantage also presents a problem: movement cancellation implies the absence of something that can be observed directly and accordingly must be estimated indirectly. A number of methods for estimating movement cancellation have been proposed (Colonius 1990;Kornylo et al 2003;Logan and Cowan 1984;Walton and Gandhi 2006). When the head is free to move, a subset of successfully cancelled gaze shifts are accompanied by small head movements to the target (Corneil and Elsley 2005).…”

A Within Trial Measure of the Stop Signal Reaction Time in a Head-Unrestrained Oculomotor Countermanding Task

“…SSRTs can also be estimated statistically using maximum likelihood methods (Kornylo et al 2003) or the density functions of the RTs from control and noncancelled STOP signal trials and the inhibition function (Colonius 1990;see Band et al 2003 for detailed description of these methods). Walton and Gandhi (2006) recently developed a novel psychophysical means of SSRT estimation by evoking blinks via air puffs. Delivering air puffs to the eye temporarily disengages the inhibition of the oculomotor burst generator.…”

“…Delivering air puffs to the eye temporarily disengages the inhibition of the oculomotor burst generator. By timing the delivery of air puffs to the peri-saccade interval, Walton and Gandhi (2006) inferred the timing of movement cancellation via the presence or absence of saccades accompanying blinks. Although statistically or behaviorally based SSRT estimates are fairly consistent, attesting to the general robustness of the race model, such estimates require the integration of results over many trials.…”

Microsaccade production during saccade cancelation in a stop-signal task

“…The saccade stop-signal task has provided tremendous insight into the neurophysiological basis of eye movements (Hanes and Schall, 1995; Hanes and Schall, 1996; Hanes and Carpenter, 1999; Cabel et al, 2000; Logan and Irwin, 2000; Asrress and Carpenter, 2001; Kornylo et al, 2003; Corneil and Elsley, 2005; Morein-Zamir and Kingstone, 2006; Walton and Gandhi, 2006; Boucher, et al, 2007; Camalier et al, 2007; Emeric et al, 2007; Joiner et al, 2007; Brown et al, 2008; Lo et al, 2009; Ray et al, 2009; Stevenson et al, 2009; Scangos and Stuphorn, 2010; Stuphorn et al, 2010; Wong-Lin et al, 2010; Pouget et al, 2011; Goonetilleke et al, 2012; Bissett and Logan, 2013; Wessel et al, 2013; Atsma, et al, 2014; Born et al, 2014; Gulberti et al, 2014). Participants are occasionally instructed to cancel saccades shortly after a cue to respond (Fig.…”