Remote distractor effects and saccadic inhibition: Spatial and temporal modulation

Abstract

The onset of a visual distractor remote from a saccade target is known to increase saccade latency (the remote distractor effect [RDE]). In addition, distractors may also selectively inhibit saccades that would be initiated about 90 ms after distractor onset (termed saccadic inhibition [SI]). Recently, it has been proposed that the transitory inhibition of saccades (SI) may underlie the increase in mean latency (RDE). In a first experiment, the distractor eccentricity was manipulated, and a robust RDE that was strongly modulated by distractor eccentricity was observed. However, the underlying latency distributions did not reveal clear evidence of SI. A second experiment manipulated distractor spatial location and the timing of the distractor onset in relation to the target. An RDE was again observed with remote distractors away from the target axis and under conditions with early-onset distractors that would be unlikely to produce SI, whereas later distractor onsets produced an RDE along with some evidence of an SI effect. A third experiment using a mixed block of target-distractor stimulus-onset asynchronies (SOAs) revealed an RDE that varied with both distractor eccentricity and SOA and changes to latency distributions consistent with the timing of SI. We argue that the notion that SI underpins the RDE is similar to the earlier argument that express saccades underlie the fixation offset (gap) effect and that changes in mean latency and to the shape of the underlying latency distributions following a visual onset may involve more than one inhibitory process.

Saccadic inhibition and the remote distractor effect: One mechanism or two?

“…In the model, early distractors are able to produce more activity because they are not competing against target activity (see Figure 3), but there is still fixation activity inhibiting them, and the distractor effects always remain less than for simultaneous distractors. This was not the case for the data in Walker and Benson (2013), where the RDEs for contralateral distractors with À60-ms SOA were equivalent to (or even larger than) those for simultaneous distractors. We therefore tested whether any simple adjustments to the model could reduce the difference between early and simultaneous distractor RDEs.…”

“…Neither our paradigm nor Walker and Benson's (2013) were ideal for directly comparing the magnitude of the RDE across SOAs. As discussed above, blocking allows differences in anticipatory, alerting, or attentional factors.…”

“…An irrelevant distractor delays saccadic latency to a target appearing in a different location (Walker, Deubel, Schneider, & Findlay, 1997). Typically a target and distractor are presented simultaneously and mean latency increases by 20 to 40 ms; error rate may also increase (Bompas & Sumner, 2009a, 2009bCasteau & Vitu, 2012;Ludwig, Gilchrist, & McSorley, 2005;Trappenberg, Dorris, Munoz, & Klein, 2001;Walker & Benson, 2013). Similar effects can occur for early distractors, presented up to around 100 ms prior to the target (though such stimuli can also carry a warning effect).…”

“…What appears to be a shift in the latency distribution for simultaneous distractors could be regarded as a dip on the leading edge of the distribution. However, other authors have argued that a mechanism transient enough to produce brief dips in the distribution would be too transient to explain the RDE from early distractors appearing 60 ms before the target (Walker & Benson, 2013); the dip would no longer be on the leading edge of the distribution, but should be finished by the time the latency distribution even starts. Therefore, a different, more sustained source of inhibition might better explain much of the RDE.…”

Norepinephrine improves attentional orienting in a predictive context

“…To assess the effect of cues and distractors on RTs in mixed runs, we computed four scores derived from the attentional network scores (Fan et al 2002) and integrating the effect of distractors (Walker and Benson 2013): alerting score, orienting score, remote distractor score and proximal distractor score. Given that these different conditions were randomly presented within runs, these scores were calculated for each run.…”