Academic journal article Attention, Perception and Psychophysics

The Control of Stimulus-Driven Saccades Is Subject Not to Central, but to Visual Attention Limitations

Academic journal article Attention, Perception and Psychophysics

The Control of Stimulus-Driven Saccades Is Subject Not to Central, but to Visual Attention Limitations

Article excerpt

In three experiments, we investigated whether the control of reflexive saccades is subject to central attention limitations. In a dual-task procedure, Task 1 required either unspeeded reporting or ignoring of briefly presented masked stimuli, whereas Task 2 required a speeded saccade toward a visual target. The stimulus onset asynchrony (SOA) between the two tasks was varied. In Experiments 1 and 2, the Task 1 stimulus was one or three letters, and we asked how saccade target selection is influenced by the number of items. We found (1) longer saccade latencies at short than at long SOAs in the report condition, (2) a substantially larger latency increase for three letters than for one letter, and (3) a latency difference between SOAs in the ignore condition. Broadly, these results match the central interference theory. However, in Experiment 3, an auditory stimulus was used as the Task 1 stimulus, to test whether the interference effects in Experiments 1 and 2 were due to visual instead of central interference. Although there was a small saccade latency increase from short to long SOAs, this difference did not increase from the ignore to the report condition. To explain visual interference effects between letter encoding and stimulus-driven saccade control, we propose an extended theory of visual attention.

Because visual acuity is high only within the small foveal area, humans need to sample their visual environments via saccadic eye movements. But how do we determine the target for future saccades? A number of behavioral (e.g., Deubel & Schneider, 1996) and single-cell studies (e.g., Kustov & Robinson, 1996; a recent review can be found in Awh, Armstrong, & Moore, 2006) support the notion that visuospatial attention plays an important role for "where to look next." Strictly speaking, it is assumed that an attention shift precedes the execution of a saccade (e.g., Findlay, 2009; Schneider, 1995). Deubel and Schneider, for example, showed that letter discrimination improves at the saccade target location just before the execution of the saccade. Similar results have been found for reflexive saccades (Schneider & Deubel, 1995, 2002).

Much less is known about the relationship between eye movement control and a second major class of attentional processes that refer to central transmodal processing (e.g., Jolicoeur, 1998). Such central attention processes are typically studied in dual-task paradigms such as the attentional blink (AB) or the psychological refractory period (PRP) paradigms. In the AB paradigm, a second target in a rapid succession of visual displays is missed when it follows the first with a short delay (e.g., Chun & Potter, 1995; Jolicoeur, 1998). In the PRP paradigm, response time (RT) to a second stimulus is prolonged when it follows a first with a short delay (e.g., Pashler, 1994). Results of AB and PRP studies have been explained by the central interference theory (CIT; e.g., Jolicoeur, 1998, 1999a; Jolicoeur & Dell'Acqua, 1998). According to CIT, cognitive processes such as response selection within the PRP or short-term consolidation (STC) within the AB paradigm require central processing. These central attention processes cannot be executed simultaneously. Thus, when one is occupied with one central process such as STC for one stimulus, central processing of a trailing stimulus has to wait; that is, response selection or consolidation for this stimulus is delayed (Jolicoeur, 1998, 1999a).

On the surface, a close relationship between central attention processes and the control of saccadic eye movements seems rather unlikely, particularly when one refers to reflexive eye movements that are triggered by the onset of a stimulus and targeted toward that stimulus. In line with these considerations, Pashler, Carrier, and Hoffman (1993) did not find the usual PRP effect for eye movements in a dual task when the participants made a saccade toward single transients. Instead, the RT prolongation was very modest. …

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