Detecting multimodality in saccadic reaction time distributions in gap and overlap tasks

In many cases the distribution of saccadic reaction times (SRT) deviates considerably from a unimodal distribution and may often exhibit several peaks. We present a statistical approach to determining the number and form of the individual peaks. The overall density of the reaction times fi…t†, i ˆ 1 F F F w obtained in w di€erent experiments with the same subject is described as the sum of u basis functions xk…t†Y k ˆ 1 F F F u with di€erent weights and an error term. A change in the experimental conditions is assumed to cause a change in the weights, not in the basis functions. We minimize the square of the di€erence (measured data minus approximation), divided by the error of the data. Incrementing u step by step we determine the necessary number of basis functions. This method is applied to data of six subjects tested in di€erent saccade tasks. We detect ®ve di€erent modes: two in the range 80±140 ms (express modes), two in the range 145±190 ms (fast-regular mode) and ...

• Type: Journal
• Year: 1998
• Where: BC
• Authors: Stefan Gezeck, Jens Timmer
• Keywords: Basis Functions, BC 1998, Data Minus Approximation, Saccadic Reaction Times