Elsevier

Human Movement Science

Volume 24, Issues 5–6, October–December 2005, Pages 744-759
Human Movement Science

Nomadic inhibition of attention and motor responses

https://doi.org/10.1016/j.humov.2005.09.007Get rights and content

Abstract

Klein and MacInnes [Klein, R. M., & MacInnes, W. J. (1999). Inhibition of return is a foraging facilitator in visual search. Psychological Science, 10, 346–352] posited that the function of a phenomenon known as the inhibition of return (IOR) [Posner, M. I., & Cohen, Y. (1984). Components of visual orienting. In H. Bouma, & D. G. Bouwhuis (Eds.), Attention and performance X: Control of language processes (pp. 531–554). Hillsdale, NJ: Erlbaum] is to facilitate the foraging of food and objects in the environment. Once a target object has been identified either the location of that target in space or a movement to that target is inhibited in order to allow the performer to shift his/her attention to something new. Interestingly, in the majority of IOR studies, participants begin their search from a central home position. This research examined IOR in a nomadic target–target paradigm in which the home position randomly appeared at one of three target locations and attentional shifts/movements progressed to other locations. In Experiment 1, participants executed simple manual button presses in response to the sequential presentation of a home position and then two target stimuli. In Experiment 2, participants made manual-aiming movements in response to the same type of presentation. Results obtained from both experiments implicate perceptual–motor mechanisms over and above the inhibition of a specific target location or response. Inhibitory effects appear to be associated with both perceptual and motor processes, and depend not only on the temporal and spatial relations between potential targets, but also on the actions required to detect or engage the targets.

Introduction

Successful orientation and survival requires rapid and accurate identification and interaction with relevant environmental stimuli. A phenomenon known as the inhibition of return (IOR) (Posner & Cohen, 1984) has been identified as a perceptual–motor process that facilitates environmental searches (Klein & MacInnes, 1999). Posner and Cohen (1984) reported a facilitated return of visually directed attention to a previously cued location when the inter-stimulus interval was short (<200 ms), and an inhibited return of visually directed attention (IOR) when the inter-stimulus interval was longer in duration (300–800 ms). This inhibitory process facilitates the visual search of novel areas. IOR has been reported for visually guided saccades (Klein & MacInnes, 1999), simple manual responses (Posner & Cohen, 1984), and goal-directed manual aiming (Tremblay, Welsh, & Elliott, 2005). The IOR effect is often small (≈20–25 ms; Taylor & Klein, 2000), but important given that the size of the effect is a large percentage of the duration of a typical visual reaction time (e.g., 180–200 ms), and of rapid reaching movements (e.g., 250–300 ms; Tremblay et al., 2005).

In the traditional IOR protocol, target boxes are located to the left and right of a central cross (e.g., Posner & Cohen, 1984). Participants fixate on the central cross for the entire trial. A trial begins with one of the two target boxes being cued. Usually this involves the outline of the target box being illuminated. Next, the central fixation cross will illuminate to draw attention back to the central location. Finally, a target will appear in one of the two target boxes. In a cue-target protocol, participants respond only to the presentation of the target, or the third stimulus. In a target–target paradigm, the first cue is presented as a target, and thus participants respond to the first and third stimulus presentations. The time between the stimulus presentations and the pattern of stimulus display can be manipulated to assess the time-course of the inhibition and facilitation. It should be noted that multiple other factors are known to influence the overall response time including the modality of the stimulus presentations (Spence, Llyod, McGlone, Nicholls, & Driver, 2000) and the effectors used in the response (Klein and MacInnes, 1999, Posner and Cohen, 1984, Tremblay et al., 2005).

A point of contention in the IOR protocol is the importance of the central fixation and central reorientation. By definition, the central fixation is a stimulus salient enough to draw attention back to the central location. Thus, by its very nature, the fixation may interfere with movement planning, attentional momentum, and the inhibitory tagging of a spatial location. IOR has been observed in attentional studies without the centring of attention (e.g., Posner and Cohen, 1984, Spalek and Hammad, 2004), however, the centring of attention within the context of manual aiming is important. In target–target manual-aiming protocols, the within trial centring of visual attention back to a central location, or fixation point is coincident with the return of the limb to the home position. Previous manual-aiming experiments exploring the IOR phenomenon have used these protocols, but have only compared trials where the participant moves from a central home position to a target in the left or right hemispace, without treating the home position as a potential target or a location to be necessarily acquired by the effector (e.g., Tremblay et al., 2005). Thus, protocols in which the hand or ocular fixation must return to a centralized home position in between responses do not explore situations in which visual attention must move from one hemispace to another, nor do they consider a reversal in attentional momentum associated with tracking the limb through space.

Klein and MacInnes (1999) have posited that the function of the IOR is to facilitate the foraging of food and objects in the environment. In their protocol, participants searched for a cue stimulus in an environment with multiple distractors and then were asked to respond to a separate target stimulus if it appeared. Participants demonstrated a tendency to conduct their search by making eye movements in the same direction as the previous saccade. Participants delayed making reversals in the direction of the previous fixation point when the target stimulus appeared in that visual space. A perceptual explanation of these findings is that the participant just observed the environment in the previous direction, and therefore they inhibit spatial locations associated with that direction. In this context, novel, previously unattended, or uncued locations are more rapidly responded to because of the lack of inhibition associated with the novel location.

Consistent with this description of the inhibition of return phenomenon are the sensory inhibition hypothesis (e.g., Berlucci, Chelazzi, & Tassinari, 2000), the motor inhibition hypothesis (e.g., Taylor and Klein, 1998, Taylor and Klein, 2000), the spreading inhibition hypothesis (e.g., Maylor & Hockey, 1985), and the inhibited hemifield hypothesis (e.g., Hughes and Zimba, 1987, Rizzolatti et al., 1987). The mechanism of the inhibition is the distinguishing feature between these proposals. The sensory inhibition hypothesis asserts that the sensory processing associated with the target location is inhibited. The motor inhibition hypothesis suggests that delays in the time to respond arise from the inhibition of motor responses to the inhibited target location. According to the spreading inhibition hypothesis, inhibition spreads out from the target location and then gets weaker as the distance from the location increases. Finally, according to the inhibited hemifield hypothesis, inhibition spreads out from the target location and then is reduced once it arrives at, or crosses a horizontal or vertical attentional meridian. Regardless of the mechanism, the basic premise from each of these models is that there exists an association of inhibition to the cued target location. The inhibition delays responses to that location and facilitates responses to novel locations.

An alternative to those involving the inhibitory tagging of a location is that there exists a motoric advantage associated with continuing a movement in the same direction as opposed to reversing direction (Brebner, 1968). This movement initiation advantage is evident in goal-directed limb movements (e.g., Helsen, Adam, Elliott, and Buekers, 2001, Experiment 2) and may also generalize to eye movements associated with a visual search. This hypothesized advantage arises from mechanisms other than those associated with the inhibition of movement planning. Consistent with this idea is the attentional momentum hypothesis (Pratt, Spalek, & Bradshaw, 1999). According to the attentional momentum hypothesis, once attention moves in a direction, it will continue in that direction until an external effort is imposed on it. The external effort can be a composite of volitional control and involuntary responses to environmental stimuli. Thus, in a traditional IOR paradigm, attention would engage the cue location, disengage the cue without inhibiting the location, be drawn towards the central fixation cue and maintain momentum in that direction. Thus responses to stimuli presented in that direction are facilitated. In this context, the protocol employed by Klein and MacInnes (1999) to examine undirected visual searches of the visual environment was different from a traditional IOR protocol because it was not necessary for participants to return their attention to a home position or a central fixation point between stimulus events (cf., Posner & Cohen, 1984). However, the protocol used by Klein and MacInnes (1999) was constrained to the extent that it did not include conditions in which attention was required to move between left and right hemispace. This type of attentional shift, which would be part of a typical visual search, has been shown to have an impact on overall inhibitory effects (e.g., Hughes & Zimba, 1987). In the study of Hughes and Zimba (1987), the reorientation of visually directed attention across the vertical and horizontal meridians caused a decrease in the time to react to visual stimuli.

Fundamental differences between simple manual responses and more complex manual-aiming responses have been shown to change the magnitude of the inhibition of the target location (Howard et al., 1999, Taylor and Klein, 1998). Arising from this notion is the consideration that the increased complexity of the required response can lead to an increase in the time prior to a response (Henry & Rogers, 1960). Following this logic, perceptual–motor differences exist between a simple visual search and a visually directed search for the guidance of manual action. Specifically, goal-directed actions require more complex coding of egocentric and allocentric space.

Given the evolutionary accounts of the inhibitory effects associated with visual selective attention, it seems important to not only study situations in which attention always returns to a central home position, but also circumstances in which attention moves from place to place in search of a target. The work reported here was designed to examine the inhibitory processes associated with nomadic searches in which the relative locations of past and future targets are important, as well as the position of the effector charged with acquiring the target. Of additional interest was the degree of movement organization required to make the response. Specifically, we were interested in whether the inhibitory effects associated with a target location depend on whether the performer must simply detect target onset (i.e., a button press), or actually perform a movement to engage the target (i.e., goal-directed aiming).

In this study, participants serially responded to three stimulus presentations. The targets were situated in a manner such that one target was located on the vertical meridian, and the other two in the right and left hemispace respectively. The presentation of the first stimulus was equally probable at each of three target locations, and therefore there was no overtly defined home location. In Experiment 1, participants executed simple manual button presses in response to the three stimulus presentations. In Experiment 2, participants quickly and accurately made manual-aiming movements to the target buttons in response to each illumination in the three-target series. The purpose of these experiments was to examine IOR in a target–target paradigm, while accounting for the centring of attention and manual response complexity between target acquisitions. Thus, these experiments were designed to study visually directed simple manual responses (Experiment 1) and manual-aiming responses (Experiment 2) without the recentring of attention to a central fixation point during a trial. Our intention was to compare and contrast the inhibitory tagging and motor facilitation models within the nomadic paradigm.

Section snippets

Participants

The participants were 20 naïve individuals (12 females, 8 males), from the McMaster university community who ranged in age from 19 to 24 years (mean = 22.1 years). This research was approved by the McMaster Research Ethics Board. All participants were right-hand dominant and had normal vision, or corrected to normal vision.

Apparatus

Custom made E-prime software presented all stimuli on a standard 40 cm computer monitor presented in the vertical position. The possible target positions consisted of three 3 cm

Experiment 2

The overall goal of this work was to examine how IOR is influenced by the interaction of movement control and environmental factors. The results of the first experiment are supportive of the notion that environmental factors influence IOR. A secondary purpose of our study was to observe potential changes in IOR with an increase in movement complexity. Thus in Experiment 2, participants executed rapid aiming movements in response to the three target illuminations.

Conclusion

Although a number of IOR papers have attempted to explain the evolutionary basis for the phenomenon in terms of processes associated with hunting and gathering, typical empirical work on the IOR involves a search that originates from a fixed home position (e.g., Pratt et al., 1999, Taylor and Klein, 2000, Tremblay et al., 2005). Even in more ecologically relevant studies in which the participant is actually required to engage the target, once it is detected, the actions directed at the target

Acknowledgments

The Natural Science and Engineering Research Council of Canada supported this research. The authors would like to thank Dr. D. Weeks and the Department of Psychology at Simon Fraser University for their hospitality during data collection (Experiment 2).

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