Against a role for attentional disengagement in the gap effect: a friendly amendment to Tam and Stelmach (1993).
Saccadic reaction time (RT) is reduced when the fixation point is removed shortly before target onset. Although Tam and Stelmach (1993) argued that this gap effect could not be explained solely by the idea that fixation offset disengaged visual attention and preferred an explanation based on disengagement of the oculomotor system, they felt that they could not rule out a hybrid model in which both oculomotor and attentional disengagement contribute to the gap effect. Our analysis of the dual response experiment (Experiment 4), upon which this hybrid model was based, shows that manual and saccadic responses were likely compromised by a grouping or delay strategy and that subjects may not have been attending as instructed. On these grounds, we argue that Tam and Stelmach (1993), like Kingstone and Klein (1990; 1993a) provide no evidence that attentional disengagement contributes to the gap effect. An alternative proposal (Klein & Kingstone, 1993), that motor preparation and oculomotor disengagement combine additively to produce the gap effect, is consistent with the data from Tam and Stelmach's Experiments 1-3, is similar to the explanation that they prefer, and has been strongly supported when directly tested (Kingstone, Klein, & Taylor, 1994).
Klein
R M
RM
Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada.
Taylor
T L
TL
Kingstone
A
A
D005403:Fixation, Ocular; D006801:Humans; D011601:Psychophysics; D011930:Reaction Time; D012438:Saccades