Social prioritisation in scene viewing and the effects of a spatial memory load.

When free-viewing scenes, participants tend to preferentially fixate social elements (e.g., people). In the present study, we tested whether this bias would be disrupted by increasing the demands of a secondary dual-task: holding a set of (one or six) spatial locations in memory, presented either simultaneously or sequentially. Following a retention interval, participants judged whether a test location was present in the to-be-remembered stimuli. During the retention interval participants free-viewed scenes containing a social element (a person) and a non-social element (an object) that served as regions of interest. In order to assess the impact of physical salience, the non-social element was presented in both an unaltered baseline version, and in a version where its salience was artificially increased. The results showed that the preference to look at social elements decreased when the demands of the spatial memory task were increased from one to six locations, regardless of presentation mode (simultaneous or sequential). The high-load condition also resulted in more central fixations and reduced exploration of the scene. The results indicate that the social prioritisation effect, and scene viewing more generally, can be affected by a concurrent memory load.

On the role of top-down and bottom-up guidance in conjunction search: Singleton interference revisited.

The current study reassessed the potential of salient singleton distractors to interfere in conjunction search. Experiment 1 investigated conjunctions of colour and orientation, using densely packed arrays that produced highly efficient search. The results demonstrated clear interference effects of singleton distractors in task-relevant dimensions colour and orientation, but no interference from those in a task-irrelevant dimension (motion). Goals exerted an influence in constraining this interference such that the singleton interference along one dimension was modulated by target relevance along the other task relevant dimension. Colour singleton interference was much stronger when the singleton shared the target orientation, and orientation interference was much stronger when the orientation singleton shared the target colour. Experiments 2 and 3 examined singleton-distractor interference in feature search. The results showed strong interference particularly from task-relevant dimensions but a reduced role for top-down, feature-based modulation of singleton interference, compared with conjunction search. The results are consistent with a model of conjunction search based on core elements of the guided search and dimension weighting approaches, whereby weighted dimensional feature contrast signals are combined with top-down feature guidance signals in a feature-independent map that serves to guide search.

Do cognitive load and ADHD traits affect the tendency to prioritise social information in scenes?

We report two experiments investigating the effect of working memory (WM) load on selective attention. Experiment 1 was a modified version of Lavie et al. and confirmed that increasing memory load disrupted performance in the classic flanker task. Experiment 2 used the same manipulation of WM load to probe attention during the viewing of complex scenes while also investigating individual differences in attention deficit hyperactivity disorder (ADHD) traits. In the image-viewing task, we measured the degree to which fixations targeted each of two crucial objects: (1) a social object (a person in the scene) and (2) a non-social object of higher or lower physical salience. We compared the extent to which increasing WM load would change the pattern of viewing of the physically salient and socially salient objects. If attending to the social item requires greater default voluntary top-down resources, then the viewing of social objects should show stronger modulation by WM load compared with viewing of physically salient objects. The results showed that the social object was fixated to a greater degree than the other object (regardless of physical salience). Increased salience drew fixations away from the background leading to slightly increased fixations on the non-social object, without changing fixations on the social object. Increased levels of ADHD-like traits were associated with fewer fixations on the social object, but only in the high-salient, low-load condition. Importantly, WM load did not affect the number of fixations on the social object. Such findings suggest rather surprisingly that attending to a social area in complex stimuli is not dependent on the availability of voluntary top-down resources.

Gatecrashing the visual cocktail party: How visual and semantic similarity modulate the own name benefit in the attentional blink.

The "visual cocktail party effect" refers to superior report of a participant's own name, under conditions of inattention. An early selection account suggests this advantage stems from enhanced visual processing. A late selection account suggests the advantage occurs when semantic information allowing identification as one's own name is retrieved. In the context of inattentional blindness (IB), Mack and Rock showed that the advantage does not generalise to a minor modification of a participant's own name, despite extensive visual similarity, supporting the late selection account. This study applied the name modification manipulation in the context of the attentional blink (AB). Participants were presented with rapid streams of names and identified a white target name, while also reporting the presence of one of two possible probes. The probe names appeared either close (the third item following the target: Lag 3) or far in time from the target (the eighth item following the target: Lag 8). The results revealed a robust AB; reports of the probe were reduced at Lag 3 relative to Lag 8. The AB was also greatly reduced for the own name compared to another name-a visual cocktail party effect. In contrast to the findings of Mack and Rock for IB, the reduced AB extended to the modified own name. The results suggest different loci for the visual cocktail party effect in the AB (word recognition) compared to IB (semantic processing).

Priming of Pop-out does not provide reliable measures of target activation and distractor inhibition in selective attention: Evidence from a large-scale online study.

Lamy, Antebi, Aviani, and Carmel (2008) reported that in a simple search task where participants located an odd coloured circle, the inter-trial relations could be used to derive robust and independent measures of target activation and distractor inhibition. When a target feature repeated there was a benefit, and when the previous target feature became the distractor feature there was a cost. These two measures correlated and were taken to reflect a measure of target activation. When the distractor feature repeated there was a benefit and when the previous distractor feature became the current target feature there was a cost, these two measures correlated and were taken to reflect a measure of distractor inhibition. In the current study we examined the same colour search task online on a large group of 312 participants. The results revealed significant effects of target and distractor repetition and switching. However, the correlations reported by Lamy et al. (2008) were non-significant. Instead we found the correlations between the two measures of repetition and the two measures of switching.

Near-independent capacities and highly constrained output orders in the simultaneous free recall of auditory-verbal and visuo-spatial stimuli.

Three experiments examined the immediate free recall (IFR) of auditory-verbal and visuospatial materials from single-modality and dual-modality lists. In Experiment 1, we presented participants with between 1 and 16 spoken words, with between 1 and 16 visuospatial dot locations, or with between 1 and 16 words and dots with synchronized onsets. We found that for dual-modality lists (a) overall performance, initial recalls, and serial position curves were largely determined by the within-modality list lengths, (b) there was only a small degree of dual-task trade-off (that was limited to the visuospatial items), and (c) there were strongly constrained output orders: participants tended to alternate between words and dots from equivalent or neighboring serial positions. In Experiments 2 and 3, we compared lists of 6 single-modality items with dual-modality lists of 6 words and 6 dots with synchronous or alternating onsets (Experiment 2), or random but asynchronous onsets (Experiment 3). In all 3 dual-modality conditions, we again found only a small trade-off in visuospatial (but not verbal) IFR performance. There were similarly highly constrained output orders with the synchronous and alternating onsets, and these patterns were present but attenuated with the randomized onsets. We propose that both auditory-verbal and visuospatial list items are associated with a common temporal episodic context that is used to guide cross-modal retrieval, and we speculate that the limited, asymmetric interference could arise because the less variable representations of the dots share only a relatively small subset of features with the more variable representations of the words. (PsycINFO Database Record

Visual search in depth: The neural correlates of segmenting a display into relevant and irrelevant three-dimensional regions.

Visual perception is facilitated by the ability to selectively attend to relevant parts of the world and to ignore irrelevant regions or features. In visual search tasks, viewers are able to segment displays into relevant and irrelevant items based on a number of factors including the colour, motion, and temporal onset of the target and distractors. Understanding the process by which viewers prioritise relevant parts of a display can provide insights into the effect of top-down control on visual perception. Here, we investigate the behavioural and neural correlates of segmenting a display according to the expected three-dimensional (3D) location of a target. We ask whether this segmentation is based on low-level visual features (e.g. common depth or common surface) or on higher-order representations of 3D regions. Similar response-time benefits and neural activity were obtained when items fell on common surfaces or within depth-defined volumes, and when displays were vertical (such that items shared a common depth/disparity) or were tilted in depth. These similarities indicate that segmenting items according to their 3D location is based on attending to a 3D region, rather than a specific depth or surface. Segmenting the items in depth was mainly associated with increased activation in depth-sensitive parietal regions rather than in depth-sensitive visual regions. We conclude that segmenting items in depth is primarily achieved via higher-order, cue invariant representations rather than through filtering in lower-level perceptual regions.

First things first: similar list length and output order effects for verbal and nonverbal stimuli.

When participants are presented with a short list of unrelated words and they are instructed that they may recall in any order, they nevertheless show a very strong tendency to recall in forward serial order. Thus, if asked to recall in any order: "hat, mouse, tea, stairs," participants often respond "hat, mouse, tea, stairs" even though there was no forward order requirement of the task. In 4 experiments, we examined whether this tendency is language-specific, reflecting mechanisms involved with speech perception, speech production, and/or verbal short-term memory. Specifically, we examined whether we would observe similar findings when participants were asked to recall, in any order, lists of between 1 and 15 nonverbal stimuli, such as visuospatial locations (Experiment 1, Experiment 3, Experiment 4), or touched facial locations (Experiment 2). Contrary to a language-specific explanation, we found corresponding tendencies (albeit somewhat reduced) in the immediate free recall of these nonverbal stimuli. We conclude that the tendency to initiate recall of a short sequence of items with the first item is a general property of memory, which may be augmented by verbal coding.

Surface-based constraints on target selection and distractor rejection: evidence from preview search.

In preview search when an observer ignores an early appearing set of distractors, there can subsequently be impeded detection of new targets that share the colour of this preview. This "negative carry-over effect" has been attributed to an active inhibitory process targeted against the old items and inadvertently their features. Here we extend negative carry-over effects to the case of stereoscopically defined surfaces of coplanar elements without common features. In Experiment 1 observers previewed distractors in one surface (1000ms), before being presented with the target and new distractors divided over the old and a new surface either above or below the old one. Participants were slower and less efficient to detect targets in the old surface. In Experiment 2 in both the first and second display the items were divided over two planes in the proportion 66/33% such that no new planes appeared following the preview, and there was no majority of items in any one plane in the final combined display. The results showed that participants were slower to detect the target when it occurred in the old majority surface. Experiment 3 held constant the 2D properties of the stimuli while varying the presence of binocular depth cues. The carry-over effect only occurred in the presence of binocular depth cues, ruling out any account of the results in terms of 2-D cues. The results suggest well formed surfaces in addition to simple features may be targets for inhibition in search.

Explaining efficient search for conjunctions of motion and form: evidence from negative color effects.

Dent, Humphreys, and Braithwaite (2011) showed substantial costs to search when a moving target shared its color with a group of ignored static distractors. The present study further explored the conditions under which such costs to performance occur. Experiment 1 tested whether the negative color-sharing effect was specific to cases in which search showed a highly serial pattern. The results showed that the negative color-sharing effect persisted in the case of a target defined as a conjunction of movement and form, even when search was highly efficient. In Experiment 2, the ease with which participants could find an odd-colored target amongst a moving group was examined. Participants searched for a moving target amongst moving and stationary distractors. In Experiment 2A, participants performed a highly serial search through a group of similarly shaped moving letters. Performance was much slower when the target shared its color with a set of ignored static distractors. The exact same displays were used in Experiment 2B; however, participants now responded "present" for targets that shared the color of the static distractors. The same targets that had previously been difficult to find were now found efficiently. The results are interpreted in a flexible framework for attentional control. Targets that are linked with irrelevant distractors by color tend to be ignored. However, this cost can be overridden by top-down control settings.

Age-of-acquisition effects in novel picture naming: a laboratory analogue.

Age-of-acquisition (AoA) effects are such that early-acquired items are more quickly recognized and produced than later acquired items. In this laboratory analogue, participants were trained to name a group of Greeble pictures with a novel nonsense name. We manipulated order of acquisition of the stimuli: Half of the stimuli were presented from the onset of training (early acquired) whilst the other half were introduced later in the training schedule (late acquired). At test, when early and late stimuli had equal cumulative frequency, early stimuli were named significantly faster than late items. In a second test, it was also found that visual duration thresholds were significantly smaller for the early items when participants were asked to name the critical items. These findings support the notion that order-of-acquisition effects can be manifest over a short time span in the laboratory, and that the effect of order of acquisition is distinct from mere frequency of exposure. The findings are consistent with the idea that AoA effects occurring over a large temporal scale may be a special case of more general order-of-acquisition effects, and both may be a general property of learning mechanisms.

The effect of age of acquisition on older individuals with and without cognitive impairments.

The present study compared the effects of age of acquisition (AoA) on object naming across groups of older individuals with cognitive impairments, healthy older controls, and young healthy controls. All participants named a set of 80 pictures, within which both AoA and frequency were manipulated orthogonally. Early-acquired objects were named faster than late-acquired objects across all groups. Response time also declined with age and with cognitive impairment between the groups. The effect of AoA differed across groups, with AoA effects being largest for the older group with cognitive impairments and smallest for the young control group. The present study adds strength to the suggestion that AoA of picture names is one of the factors that influence survival or loss of memories in dementia and cognitive decline, and this could therefore be used as a potential screening test for cognitive impairment disorders in the future.

Parallel distractor rejection as a binding mechanism in search.

The relatively common experimental visual search task of finding a red X amongst red O's and green X's (conjunction search) presents the visual system with a binding problem. Illusory conjunctions (ICs) of features across objects must be avoided and only features present in the same object bound together. Correct binding into unique objects by the visual system may be promoted, and ICs minimized, by inhibiting the locations of distractors possessing non-target features (e.g., Treisman and Sato, 1990). Such parallel rejection of interfering distractors leaves the target as the only item competing for selection; thus solving the binding problem. In the present article we explore the theoretical and empirical basis of this process of active distractor inhibition in search. Specific experiments that provide strong evidence for a process of active distractor inhibition in search are highlighted. In the final part of the article we consider how distractor inhibition, as defined here, may be realized at a neurophysiological level (Treisman and Sato, 1990).

Integrating space and time in visual search: how the preview benefit is modulated by stereoscopic depth.

We examined visual search for letters that were distributed across both 3 dimensional space, and time. In Experiment 1, when participants had foreknowledge of the depth plane and time interval where targets could appear, search was more efficient if the items could be segmented either by depth or by time (with a 1000 ms preview), and there were increased benefits when the two cues (depth and time) were combined. In Experiments 2 and 3 the target depth plane was always unknown to the participant. In this case, depth cues alone did not facilitate search, though they continued to increase the preview benefit. In Experiment 4 new items in preview search could fall at the same depth as preview items or a new depth. There was a substantial cost to search if the target appeared at a previewed depth. Experiment 5 showed that this cost remained even when participants knew the target would appear at the old depth on 75% of trials. The results indicate that spatial (depth) and temporal cues combine to enhance visual segmentation and selection, and this is accomplished by inhibition of distractors in irrelevant depth planes.

Inhibitory guidance in visual search: the case of movement-form conjunctions.

We used a probe-dot procedure to examine the roles of excitatory attentional guidance and distractor suppression in search for movement-form conjunctions. Participants in Experiment 1 completed a conjunction (moving X amongst moving Os and static Xs) and two single-feature (moving X amongst moving Os, and static X amongst static Os) conditions. "Active" participants searched for the target, whereas "passive" participants viewed the displays without responding. Subsequently, both groups located (left or right) a probe dot appearing in either an occupied or an unoccupied location. In the conjunction condition, the active group located probes presented on static distractors more slowly than probes presented on moving distractors, reversing the direction of the difference found within the passive group. This disadvantage for probes on static items was much stronger in conjunction than in single-feature search. The same pattern of results was replicated in Experiment 2, which used a go/no-go procedure. Experiment 3 extended the go/no-go procedure to the case of search for a static target and revealed increased probe localisation times as a consequence of active search, primarily for probes on moving distractor items. The results demonstrated attentional guidance by inhibition of distractors in conjunction search.

Spreading suppression and the guidance of search by movement: evidence from negative color carry-over effects.

A growing number of studies have shown that significant impairments to search and selection can occur if the target item carries a feature of the irrelevant distractors currently being ignored Braithwaite, Humphreys, and Hodsoll (Journal of Experimental Psychology: Human Perception and Performance, 29, 758-778, 2003). However, these effects have been documented only when search has been extended over time (i.e., in preview search), and not in standard search displays with simultaneously presented items. Here, we present the first evidence that similar costs to selection can occur in simultaneous displays under appropriate circumstances. In the present experiment, participants searched a display for a moving target letter among static and moving distractors. Search efficiency was significantly enhanced for a moving target when half of the letters moved (and half remained static), allowing the static items to be excluded from search. However, if the moving target then shared its color with the irrelevant static items, significant costs emerged, relative to baselines. These results are consistent with the involvement of a general feature-based suppression mechanism in selection, operating over space as well as time.

Comparing segmentation by time and by motion in visual search: an FMRI investigation.

Brain activity was recorded while participants engaged in a difficult visual search task for a target defined by the spatial configuration of its component elements. The search displays were segmented by time (a preview then a search display), by motion, or were unsegmented. A preparatory network showed activity to the preview display, in the time but not in the motion segmentation condition. A region of the precuneus showed (i) higher activation when displays were segmented by time or by motion, and (ii) correlated activity with larger segmentation benefits behaviorally, regardless of the cue. Additionally, the results revealed that success in temporal segmentation was correlated with reduced activation in early visual areas, including V1. The results depict partially overlapping brain networks for segmentation in search by time and motion, with both cue-independent and cue-specific mechanisms.

Neuropsychological evidence for a competitive bias against contracting stimuli.

Two experiments examined extinction to stimuli presented either with contracting or expanding motion. Experiment 1 used solid shapes which either increased or decreased in size rapidly, consistent with looming motion. Experiment 2 employed random dots so that stimulus size was not confounded with type of motion. In both experiments extinction was modulated by the type of motion presented, with extinction most evident when a contracting object was in the weaker visual field. In addition, in Experiment 2 there was evidence for grouping modulating extinction, when there were looming stimuli in both fields. The results suggest that looming motion is a powerful determinant of stimulus salience in selective attention.

Deficits in visual search for conjunctions of motion and form after parietal damage but with spared hMT+/V5.

It has been argued that area hMT+/V5 in humans acts as a motion filter, enabling targets defined by a conjunction of motion and form to be efficiently selected. We present data indicating that (a) damage to parietal cortex leads to a selective problem in processing motion-form conjunctions, and (b) that the presence of a structurally and functional intact hMT+/V5 is not sufficient for efficient search for motion-form conjunctions. We suggest that, in addition to motion-processing areas (e.g., hMT+/V5), the posterior parietal cortex is necessary for efficient search with motion-form conjunctions, so that damage to either brain region may bring about deficits in search. We discuss the results in terms of the involvement of the posterior parietal cortex in the top-down guidance of search or in the binding of motion and form information.