Chiau HY, Tseng P, Su JH, Tzeng OJ, Hung DL, Muggleton NG, Juan CH. Trial type probability modulates the cost of antisaccades. J Neurophysiol 106: 515-526, 2011. First published May 4, 2011 doi:10.1152/jn.00399.2010The antisaccade task, where eye movements are made away from a target, has been used to investigate the flexibility of cognitive control of behavior. Antisaccades usually have longer saccade latencies than prosaccades, the so-called antisaccade cost. Recent studies have shown that this antisaccade cost can be modulated by event probability. This may mean that the antisaccade cost can be reduced, or even reversed, if the probability of surrounding events favors the execution of antisaccades. The probabilities of prosaccades and antisaccades were systematically manipulated by changing the proportion of a certain type of trial in an interleaved pro/antisaccades task. We aimed to disentangle the intertwined relationship between trial type probabilities and the antisaccade cost with the ultimate goal of elucidating how probabilities of trial types modulate human flexible behaviors, as well as the characteristics of such modulation effects. To this end, we examined whether implicit trial type probability can influence saccade latencies and also manipulated the difficulty of cue discriminability to see how effects of trial type probability would change when the demand on visual perceptual analysis was high or low. A mixed-effects model was applied to the analysis to dissect the factors contributing to the modulation effects of trial type probabilities. Our results suggest that the trial type probability is one robust determinant of antisaccade cost. These findings highlight the importance of implicit probability in the flexibility of cognitive control of behavior.saccade; visual attention; voluntary control IN THE EVER-CHANGING WORLD, probabilistic information relating to the surrounding environment is actively utilized by individuals to adapt their behaviors flexibly to achieve their goals. The saccadic eye movement system is an excellent model for studying the flexibility of human behavior because it is conducive to measurement in the laboratory and has been well characterized on a neurophysiological basis (Hutton 2008;Munoz and Everling 2004). The effects of prior probabilistic information on saccadic performance have been well documented. For example, gaze is directed to specific locations faster when they represent higher likelihoods of target presence based on past experience (e.g., Carpenter and Williams 1995;Gmeindl et al. 2005;Liu et al. 2010;Miller 1988;Milstein and Dorris 2007; for recent reviews see Angelaki et al. 2009;Summerfield and Egner 2009). Most importantly, this utilization of probabilistic information is not constrained at the simple stimulus-and-response level, because it can also be observed when the task requires visual analysis and response selection. Recently, Liu et al. (2010) used a central cue to indicate to participants whether they should saccade to (prosaccade) or away from ...

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Predictability in the visual environment provides a powerful cue for efficient processing of scenes and objects. Recently, studies have suggested that the directionality and magnitude of saccade curvature can be informative as to how the visual system processes predictive information. The present study investigated the role of the right posterior parietal cortex (rPPC) in shaping saccade curvatures in the context of predictive and non-predictive visual cues. We used an orienting paradigm that incorporated manipulation of target location predictability and delivered transcranial magnetic stimulation (TMS) over rPPC. Participants were presented with either an informative or uninformative cue to upcoming target locations. Our results showed that rPPC TMS generally increased saccade latency and saccade error rates. Intriguingly, rPPC TMS increased curvatures away from the distractor only when the target location was unpredictable and decreased saccadic errors towards the distractor. These effects on curvature and accuracy were not present when the target location was predictable. These results dissociate the strong contingency between saccade latency and saccade curvature and also indicate that rPPC plays an important role in allocating and suppressing attention to distractors when the target demands visual disambiguation. Furthermore, the present study suggests that, like the frontal eye fields, rPPC is critically involved in determining saccade curvature and the generation of saccadic behaviors under conditions of differing target predictability.

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