Coordination of component mental operations in a multiple-response task

Models of human performance typically focus on the mental components of task processing from discrete task trials. This approach neglects the advance planning of actions and overlapping of tasks characteristic of natural settings. The present research measures the joint timing of eye movements and manual responses in a typing-like task with the goal of extending models of discrete task performance to continuous domains. Following Pashler [1994] participants made separate choice responses to a series of five letters spread over a wide viewing area. Replicating Pashler's results, significant preview effects were found in both response time and eye movement data. Response to the first stimulus was delayed, with inter-response intervals for subsequent items rapid and flat across items. The eyes moved toward the next letter about 800 ms before the corresponding manual response (eye-hand span). Fixation dwell time was affected by stimulus luminance as well as difficulty of response mapping. The results suggest that fixation duration entails more than perceptual analyses. Implications of the results are discussed.