Cognitive Techniques Investigating Spatial Attention

To date, the majority of studies investigating visual attentional bias have focused on the spatial domain (e.g., see Carrasco, 2011; Peterson & Posner, 2012 for reviews). Below follows a brief review of the three most utilised paradigms.

2.3.1 Visual Search

One paradigm that has been employed to investigate spatial attentional bias is the visual search task (Hansen & Hansen, 1988; Öhman, Flykt, & Esteves, 2001). This involves presenting a target stimulus embedded in an array of distracting stimuli. For example, a threatening face is presented in a matrix (typically a four row by four column pattern) of neutral or positive faces; conversely, a neutral or positive face is embedded in a matrix of threatening faces. Participants are required to search for and identify the target stimulus as quickly and as accurately as possible. Attentional bias can be indicated by faster response times to detect threat-related targets embedded in an array of neutral or positive faces compared with neutral or positive targets embedded in an array of threatening faces. Cisler and Koster (2010) have suggested that this demonstrates facilitated engagement to threat.

20 Attentional bias can also be indicated by slower response times to detect neutral or positive targets embedded in an array of threatening faces compared with neutral or positive targets embedded in an array of neutral or positive faces. This is thought to demonstrate difficulties in disengagement from threat (Cisler & Koster, 2010). However, a limitation of the visual search task is that young children find it difficult to effectively monitor across multiple possible target dimensions (Donnelly et al., 2007; Gerhardstein & Rovee-Collier, 2002; Trick & Enns, 1998). Additionally, the visual search task has been criticised with the argument that attentional bias may be goal dependent because participants are directly instructed to search for either a positive or a threatening face (Smith et al., 2006).

2.3.2 Spatial Cueing

A further paradigm that has been utilised to investigate spatial biases of attention is the spatial cueing task (Fox, Russo, Bowles, & Dutton, 2001). Based on Posner’s cueing paradigm (1980), this involves participants focusing on a central fixation point whilst a single cue is presented in one of two locations (e.g., left or right). This is then followed by a single target that appears at either the same location as the cue (a congruent trial) or at the opposite location (an incongruent trial). Participants are required to respond to the target as quickly and as accurately as possible. In the emotive version of the task, schematic or photographic pictures of threatening (e.g., angry), happy, or neutral faces are included as the cues (e.g., Fox, Russo, & Dutton, 2002; Verkuil, Brosschot, Putman, & Thayer, 2009). Attentional bias is inferred from faster response times on congruent threat-cued trials relative to neutral- or positive-cued trials. Attentional bias is also inferred from slower response times on incongruent threat-cued trials relative to neutral- or positive-cued trials. A criticism of the spatial cueing task is that it involves presenting only one stimulus prior to the target. This means that any differences in the initial tendency to prioritise attention for one stimulus over another cannot be determined. Thus, the spatial cueing task is limited in that it can only be employed to investigate the disengagement component of attentional bias (Fox et al., 2002). Furthermore, incorporating just one stimulus limits ecological validity since it does not offer a method of investigating competition between stimuli (Bar-Haim, Lamy, Pergamin, Bakermans-Kranenburg, & van Ijzandoorn, 2007).

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2.3.3 Visual Probe

The visual probe (VP; MacLeod, Mathews, & Tata, 1986) task is now the most frequently applied methodology utilised to explore the effects of anxiety on spatial biases of attention (Staugaard, 2010). In a typical version of the VP task, a pair of stimuli (e.g., facial expressions) flanks a central fixation on a visual display (e.g., computer monitor). One of the stimuli is emotive (e.g., an angry or happy facial expression) and the other is neutral. The pair is presented briefly (typically for 500 ms; see Mogg & Bradley, 1998 for a review) before vanishing and being replaced immediately by a probe (e.g., an asterisk or a dot). The probe appears in one of the locations previously occupied by a stimulus; it can appear in the place of the emotive or the neutral stimulus. This is done in a semi-randomised sequence to ensure that probes are counter-balanced, that is, replace an equal number of emotive and neutral faces presented above and below / to the left and right of the fixation. Trials in which the probe appears in the place of the emotive stimulus are known as ‘congruent’ and trials in which the probe appears in the place of the neutral stimulus are known as ‘incongruent’. Participants are then required to respond to the probe as quickly and as accurately as possible either by indicating when the probe appears or by classifying its location (e.g., left vs. right) / type (e.g., : vs. ..), depending on the task version. It is hypothesised that individuals respond more rapidly to a probe when it appears in an attended, as opposed to an unattended, spatial location (Posner, Snyder, & Davidson, 1980). Thus, a fast reaction time to a congruent, compared to an incongruent, trial indicates enhanced attention to an emotive stimulus and/or diminished attention to a neutral stimulus. In contrast, a slow reaction time to a congruent, compared to an incongruent, trial indicates diminished attention to an emotive stimulus and/or enhanced attention to a neutral stimulus.

The VP task has several advantages over other paradigms that measure spatial attentional bias. For example, it is more suited to the presentation of pictorial stimuli compared with other measures. Facial stimuli are increasingly being incorporated in attentional bias tasks because it is understood that faces are especially meaningful and salient for humans (Adolphs, 2002, 2003; Darwin, 1872; Ekman & Friesen, 1969; Kolassa et al., 2009; Öhman, 1996), thus allowing for greater ecological validity. Another advantage of the VP task is that it encourages competition among stimuli, which may be a prerequisite for attentional bias to emerge (Bar-Haim et al., 2007). This is because multiple stimuli often compete for our attention in the natural environment. Therefore, the VP task may be a more sensitive measure of spatial attention than paradigms that utilise single stimulus presentation

22 such as the spatial cueing task. Furthermore, the VP task allows for manipulation of the stimulus onset asynchrony (i.e., the time interval between stimuli and probe presentation), meaning that the time course of attentional allocation can be investigated.

However, a limitation of the VP task is that it provides just a snap-shot of attentional allocation at a specified time-point. In other words, the measure is not sensitive to participants’ shifts in attention that may occur repeatedly throughout the duration of each trial (Caseras, Garner, Bradley, & Mogg, 2007), especially when longer stimulus durations are employed. Consequently, it is beneficial to combine the VP task with eye tracking (ET) technology.

2.3.4 Visual Probe with Eye Tracking

ET provides a continuous measure of the exact position of eye gaze, making it one of the most direct methods of investigating overt attention (Bögels & Mansell, 2004). Furthermore, this method offers greater ecologically validity (Caseras et al., 2007), since the direction of gaze is closely linked to what one perceives (Aslin & McMurray, 2004). ET provides measures of initial orienting (as reflected by the direction and latency of the first shift in gaze) and maintenance / shifts of attention (as indexed by gaze duration). As such, this methodology is able to help determine whether participants initially attend to a particular stimulus type, remain fixed on a specific stimulus type, shift attention back and forth in an unstable manner (e.g., Garner, Mogg, & Bradley, 2006), or avoid stimuli at longer presentation times (Frewen, Dozois, Joanisse, & Neufeld, 2008). This makes ET an effective methodology for testing the vigilance-avoidance theory (Mogg & Bradley, 1998; Mogg, Bradley, de Bono, & Painter, 1998; Mogg, Mathews, & Weinman, 1987) [described in

Chapter 7, section 7.1].