The relationship between attentional capture and deviations in movement trajectories in a selective reaching task

Abstract

According to action-centered models of attention, attention and action systems are tightly linked such that the capture of attention by an object automatically initiates response-producing processes. In support of this link, studies have shown that movements deviate towards or away from non-target stimuli. These deviations are thought to emerge because attentional capture by non-target stimuli generates responses that summate with target responses to develop a combined movement vector. The present study tested attention–action coupling by examining movement trajectories in the presence of non-target stimuli that do or do not capture attention. Previous research has revealed that non-target cue stimuli only capture attention when they share critical features with the target. Cues that do not share this feature do not capture attention. Following these studies and their findings, participants in the present study aimed to the location of a single white square (onset singleton target) or a single red square presented with two white squares (color singleton target). In separate blocks, targets were preceded by non-predictive cues that did or did not share the target feature (color or onset singleton cues). The critical finding of the present study was that trajectory effects mirrored the temporal interference effects in that deviations were only observed when cue and target properties matched. Deviations were not observed when the cue and target properties did not match. These data provide clear support for the link between attentional capture and the activation of response-producing processes.

Introduction

There is an extensive literature on the relationship between attention and goal-directed (saccadic) eye movements on both behavioral (e.g., Deubel & Schneider, 1996) and neural (e.g., Goldberg et al., 2006, McPeek, 2006) levels of analysis. The possible links between attention and hand movements, on the other hand, have received more modest consideration. A growing series of recent studies, however, has been conducted to investigate the interactions between attention and manual motor systems (e.g., Bekkering and Neggers, 2002, Fagioli et al., 2007, Linnell et al., 2005, Schiegg et al., 2003, Tipper et al., 1992, Welsh and Pratt, 2008). This developing line of research on attention and limb movements emerged because of: 1) evidence of a significant overlap and integration of cortical areas responsible for attention and action planning (see Cisek, 2006, Rizzolatti et al., 1994 for reviews); and, 2) the realization that the attention system developed through evolution to provide information for the production of goal-directed limb movements, such as aiming and grasping, and not the relatively arbitrary keypress responses usually employed in studies of selective attention (Allport, 1987).

These more recent studies have lead to the development of action-centered theories and models of attention (e.g., Rizzolatti et al., 1994, Tipper et al., 1992). The main tenet of action-centered attention is that the processes of attention and action are so tightly linked that: 1) the distribution and capture of attention is determined, in part, by the to-be-performed action (Tipper et al., 1992, Welsh and Pratt, 2008); and, 2) that the capture of attention by a particular object automatically activates response producing processes that are generated to allow the individual to interact with the object (Tipper et al., 1992, Tipper et al., 1999, Welsh et al., 1999). The purpose of the present study was to test the latter by examining the trajectories of manual aiming movements completed in conditions in which the same set of stimuli do, or do not, capture attention.

To elucidate, the main evidence supporting the idea that attentional capture leads to the activation of response producing processes comes from studies showing that the characteristics of goal-directed limb movements are affected by the presence of distracting, non-target stimuli (e.g., Lee, 1999, Song and Nakayama, 2006, Song and Nakayama, 2008, Tipper et al., 1999, Welsh et al., 1999). Specifically, it has been reported that the trajectories of aiming movements veer towards (Welsh et al., 1999, Welsh and Elliott, 2004) or away from (Howard and Tipper, 1997, Welsh and Elliott, 2004) the location of non-target stimulus information. It has been suggested that these trajectory deviations occur because the capture of attention by target and non-target stimuli automatically activates a response code to each stimulus. When aiming responses are required, it is suggested that these independent target and non-target responses are represented, in part, by the activation of different subpopulations of directionally-tuned cells (Georgopoulos, 1990). The initial direction of the movement is then determined by the resultant vector of these simultaneously represented responses (Cisek and Kalaska, 2002, Cisek and Kalaska, 2005) at the moment of movement initiation (Erlhagen and Schöner, 2002, Tipper et al., 1999, Welsh et al., 1999).

Although there are different explanations of the mechanisms that cause the specific pattern of deviations towards or away from a non-target that have been observed, there is general consensus that the deviations occur because the resultant movement code reflects the current activation state of both target and non-target response codes—deviations towards a non-target reveals that the non-target response representation is active, whereas deviation away from a target reveals that the non-target response representation has been inhibited (e.g., Howard and Tipper, 1997, Tipper et al., 1999, Welsh and Elliott, 2004; see Welsh & Weeks, 2010 for a recent review). The important premise of each explanation for the present paper is that the activation of competing response codes are dependent on attentional capture by the non-target stimuli. Without attentional capture by the non-target stimulus, there will be no competing response code and no trajectory deviations. The present study was designed to test this entry point hypothesis by examining the relationship between attentional capture and trajectory deviations.

To this end, an adaptation of the contingent involuntary orienting task (Folk, Remington, & Johnston, 1992) was used because it provided an established method for the study of property-specific attentional capture (i.e., contexts in which the same stimuli do and do not capture attention). Participants in the Folk et al. (1992) study were asked to identify a target presented at one of four locations with a keypress response. The target for a given trial was either an onset singleton (only a single stimulus presented) or a color singleton (a red target stimulus presented amongst a series of white non-target stimuli). On the most theoretically-relevant trials, the target display was preceded by a cue display in which the properties of the cue matched the target (e.g., an onset singleton cue followed by an onset singleton target) or did not match the target (e.g., an onset singleton cue followed by a color singleton target). The cue was presented either at the same location as the subsequent target (cued-target trial) or at a different location (uncued-target trial) from the target. The critical finding was that an interference effect associated with cues presented at a different location from the target was only observed when the properties of the cue matched the properties of the target. Specifically, interference effects (an increase in response times on uncued target trials thought to be associated with attentional capture by the cue) were observed when the onset singleton target was preceded by an onset singleton cue, but not when preceded by a color singleton cue. Likewise, interference effects were observed when the color singleton target was preceded by a color singleton cue, but not when preceded by an onset singleton cue. Folk et al., 1992, Folk et al., 1994 and others (e.g., Gibson & Kelsey, 1998) have argued that this pattern of interference occurs because people are able to establish a top–down “attentional set” that permits stimuli that match the searched-for (i.e., target) property to capture attention and receive more in depth processing. Stimuli whose properties do not match this attentional set do not capture attention. Thus, it was suggested that the interference effects were only observed when the cue properties matched the attentional set because the cue stimuli that matched the attentional set captured attention and competed with the target stimuli for cognitive resources. Cue stimuli not matching the attentional set did not capture attention and, hence, did not compete with the target stimuli for resources.

The present study exploited the feature-specific nature of attentional capture to test the relationship between attentional capture and trajectory deviations. Participants were asked to complete rapid aiming movements to one of three target locations identified by either a color or an onset singleton stimulus. The target was preceded by a singleton cue stimulus that either matched or did not match the property of the target stimulus (e.g., Folk et al., 1992). The location of the target and cue stimuli were randomized within a block of trials such that the targets and cues were presented at the same location (cued-target trials) on some trials and the cue and target were presented at different locations (uncued-target trials) on other trials. There was also a no cue trial condition in which only the target appeared.

If, as predicted through action-centered attention models of attention, the capture of attention by a stimulus automatically activates response codes to interact with that stimulus, then trajectory deviations will only be observed in cue-target conditions in which the cue stimulus captures attention and causes temporal interference effects. Based on the contingent capture hypothesis and findings of Folk et al., 1992, Folk et al., 1994, it was expected that cue stimuli will only capture attention and cause temporal and trajectory interference effects when the properties of the cue stimuli match the properties of the target stimuli because they fit with the attentional set (i.e., onset singleton cue-onset singleton target and color singleton cue-color singleton target trial blocks). In contrast, because stimuli not matching the attentional set are not likely to capture attention, then temporal and trajectory interference effects should not be observed in trial blocks on which onset singleton cues precede color singleton targets or color singleton cues precede onset singleton targets. Any pattern of findings in which temporal and trajectory effects are not observed in exactly the same conditions would contradict the tenet of action-centered models of attention that the capture of attention by a stimulus drives a response-producing process to interact with that stimulus. Such a set of findings would suggest that the link between attention and action is weaker than proposed and that the activation of motor plans may be relatively independent from attentional capture.