Saccadic latencies are conventionally viewed as reflecting the accumulation of information during decision-making process. However, we have previously shown that latency distributions may be strongly affected by reinforcement contingencies (Madelain et al., 2007). Here, we probe the effect of concurrent schedules on the control of saccadic latencies.
Six human adults made saccades within 80-300ms following the horizontal displacement of a target. For each subject, we selected two classes of latencies, ‘short’ and ‘long’, using the first and last quartiles of baseline distribution (e.g. [80;151]ms and [185;300]ms respectively). Applying random interval reinforcement schedules, we then concurrently reinforced each class in three blocked conditions (approximately 20000 saccades per subject) such that the relative frequencies of reinforcing ‘short’ versus ‘long’ latencies were either 9/1, 1/9 or 1/1.
We observed modifications of latency distributions depending on the reinforcement contingency in force: distributions shifted toward the shorter or longer values or became strongly bimodal and the relative proportion of latencies matched the relative proportion of reinforcers earned from each option (sensitivity up to 0.95).
Our results indicate that learned contingencies might considerably affect the allocation of saccades in time, and provide strong evidence of a control of saccadic latencies extending well beyond information accumulation.