Medium versus difficult visual search: How a quantitative change in the functional visual field leads to a qualitative difference in performance.

The dominant theories of visual search assume that search is a process involving comparisons of individual items against a target description that is based on the properties of the target in isolation. Here, we present four experiments that demonstrate that this holds true only in difficult search. In medium search it seems that the relation between the target and neighbouring items is also part of the target description. We used two sets of oriented lines to construct the search items. The cardinal set contained horizontal and vertical lines, the diagonal set contained left diagonal and right diagonal lines. In all experiments, participants knew the identity of the target and the line set used to construct it. In difficult search this knowledge allowed performance to improve in displays where only half of the search items came from the same line set as the target (50% eligibility), relative to displays where all items did (100% eligibility). However, in medium search, performance was actually poorer for 50% eligibility, especially on target-absent trials. This opposite effect of ineligible items in medium search and difficult search is hard to reconcile with theories based on individual items. It is more in line with theories that conceive search as a sequence of fixations where the number of items processed during a fixation depends on the difficulty of the search task: When search is medium, multiple items are processed per fixation. But when search is difficult, only a single item is processed.

The role of transients in action observation.

A large number of studies have now described the various ways in which the observation of another person's dynamic movement can influence the speed with which the observer is able to prepare a motor action themselves. The typical results are most often explained with reference to theories that link perception and action. Such theories argue that the cognitive structures associated with each share common representations. Consequently, action preparation and action observation are often said to be functionally equivalent. However, the dominance of these theories in explaining action observation effects has masked the potential contribution from processes associated with the detection of low-level "transients" resulting from observing a body movement, such as motion and sound. In the present review, we describe work undertaken in one particular action observation phenomenon ("social inhibition of return") and show that the transient account provides the best explanation of the effect. We argue that future work should consider attention capture and orienting as a potential contributing factor to action observation effects more broadly.

Are goal states represented during kinematic imitation?

A number of studies have shown that observation of another person's actions can modulate one's own actions, such as when 2 individuals cooperate in order to complete a joint task. However, little is known about whether or not direct matching of specific movements is modulated by the goals of the actions observed. In a series of 7 experiments, we employed an action observation paradigm in which 2 coactors sat opposite each other and took turns to reach out to targets presented on a shared workspace. Importantly, coactors performed either the same goal at the reached-to location or a different goal. Although results consistently showed that the reaching action of 1 individual slows the observer's reaching action to the same spatial location, the effect was not modulated according to the adopted goals of coactors. These findings challenge the notion that the processes involved in the imitation of specific movements code for the action goals of those movements. (PsycINFO Database Record

Response-specific effects in a joint action task: social inhibition of return effects do not emerge when observed and executed actions are different.

Although the inhibition of return (IOR) effect is primarily studied when people act individually, IOR is also observed in social environments where a person observes a partner's response before executing their own response (social or sIOR). Specifically, an observer takes longer to initiate a response to a target at a location that another individual has just responded to than to another location. The present study was conducted to determine if sIOR emerges when two individuals execute different actions-one participant executed keypress responses and the other completed aiming movements to the same set of stimuli. The two conditions in the present experiment were designed to separate the effects of observing a co-actor's target information from observing their subsequent response. In the Full Vision condition, observers saw both the target stimuli and the response of the partner. In the Partial Vision condition, observers witnessed the response of the partner, but did not see the target stimulus or any other potentially attention capturing event at the target location. It was found that, although sIOR emerged in the Full Vision condition, sIOR did not emerge in the Partial Vision condition. These and other previous findings on the impact of action goal on sIOR are discussed with reference to the potential contributions of attention and action co-representation mechanisms to the sIOR effect.

Action or attention in social inhibition of return?

When two individuals alternate reaching responses to targets located in a visual display, reaction times are longer when responses are directed to where the co-actor just responded. Although an abundance of work has examined the many characteristics of this phenomenon it is not yet known why the effect occurs. In particular, some authors have argued that action representation mechanisms are central to the effect. However, here we present evidence in support of an account in which the representation of action is not necessary. First, the basic effect occurs even when participants cannot see their co-actor's movement but, importantly, have their attention shifted to a target side via an attentional cue. Second, its time course is too short-lasting to function effectively as a component of action planning. Finally, unlike other joint action phenomena, the effect is not modulated by higher order mechanisms concerned with the personal attributes of a co-actor. Taken together, these results suggest that this particular joint action phenomenon is due to attentional rather than action mechanisms.

Peripheral cues and gaze direction jointly focus attention and inhibition of return.

Centrally presented gaze cues typically elicit a delayed inhibition of return (IOR) effect compared to peripheral exogenous cues. We investigated whether gaze cues elicit early onset IOR when presented peripherally. Faces were presented in the left or right peripheral hemifields, which then gazed upward or downward. A target appeared in one of four oblique spatial locations giving the cue and target horizontal or vertical congruency, both, or neither. After establishing that peripheral movement and gaze direction jointly facilitate target processing at short durations (200 ms: Experiment 1), IOR was evident for peripheral motion at longer time courses (800 and 2400 ms: Experiment 2). Only after 2400 ms did gaze direction additionally contribute to IOR for the specific gazed at location, showing the inverse pattern of response times to Experiment 1. The onset of IOR for gaze cues is independent from peripheral exogenous cueing but nevertheless contributes to the allocation of attention.

When your decisions are not (quite) your own: action observation influences free choices.

A growing number of studies have begun to assess how the actions of one individual are represented in an observer. Using a variant of an action observation paradigm, four experiments examined whether one person's behaviour can influence the subjective decisions and judgements of another. In Experiment 1, two observers sat adjacent to each other and took turns to freely select and reach to one of two locations. Results showed that participants were less likely to make a response to the same location as their partner. In three further experiments observers were asked to decide which of two familiar products they preferred or which of two faces were most attractive. Results showed that participants were less likely to choose the product or face occupying the location of their partner's previous reaching response. These findings suggest that action observation can influence a range of free choice preferences and decisions. Possible mechanisms through which this influence occurs are discussed.

Is social inhibition of return due to action co-representation?

When two individuals alternate reaching responses to visual targets presented on a shared workspace, one individual is slower to respond to targets occupying the same position as their partner's previous response. This phenomenon is thought to be due to processes that inhibit the initiation of a movement to a location recently acted upon. However, two distinct forms of the inhibition account have been posited, one based on inhibition of an action, the other based on inhibition of an action and location. Furthermore, an additional recent explanation suggests the phenomenon is due to mechanisms that give rise to action congruency effects. Thus the three different theories differ in the degree to which action co-representation plays a role in the effect. The aim of the present work was to examine these competing accounts. Three experiments demonstrated that when identical actions are made, the effect is modulated by the configuration of the visual stimuli acted upon and the perceptual demands of the task. In addition, when the co-actors perform different actions to the same target, the effect is still observed. These findings support the hypothesis that this particular joint action phenomenon is generated via social cues that induce location-based inhibition of return rather than being due to shared motor co-representations.

Looming motion primes the visuomotor system.

A wealth of evidence now shows that human and animal observers display greater sensitivity to objects that move toward them than to objects that remain static or move away. Increased sensitivity in humans is often evidenced by reaction times that increase in rank order from looming, to receding, to static targets. However, it is not clear whether the processing advantage enjoyed by looming motion is mediated by the attention system or the motor system. The present study investigated this by first examining whether sensitivity is to looming motion per se or to certain monocular or binocular cues that constitute stereoscopic motion in depth. None of the cues accounted for the looming advantage. A perceptual measure was then used to examine performance with minimal involvement of the motor system. Results showed that looming and receding motion were equivalent in attracting attention, suggesting that the looming advantage is indeed mediated by the motor system. These findings suggest that although motion itself is sufficient for attentional capture, motion direction can prime motor responses.

Visual cognition during real social interaction.

Laboratory studies of social visual cognition often simulate the critical aspects of joint attention by having participants interact with a computer-generated avatar. Recently, there has been a movement toward examining these processes during authentic social interaction. In this review, we will focus on attention to faces, attentional misdirection, and a phenomenon we have termed social inhibition of return (Social IOR), that have revealed aspects of social cognition that were hitherto unknown. We attribute these discoveries to the use of paradigms that allow for more realistic social interactions to take place. We also point to an area that has begun to attract a considerable amount of interest-that of Theory of Mind (ToM) and automatic perspective taking-and suggest that this too might benefit from adopting a similar approach.

Do action goals mediate social inhibition of return?

Social inhibition of return is the phenomenon whereby an individual is slower to reach to locations to which another individual has recently responded. Although this suggests that an observer represents another person's action, little is known about which aspects of the action are encoded. The present work describes a series of three experiments examining whether social inhibition of return represents the endpoint goal of the action, i.e., is 'goal based'. Pairs of participants sat opposite to one another and alternated responses to a cued or non-cued object presented on a table top. Importantly, either the two participants performed the same interaction with the object or a different interaction. Although all our experiments showed social inhibition of return, the size of the effect was not modulated according to whether each participant had the same or different goal. We conclude that although the mechanisms giving rise to social inhibition of return do encode some aspects of a response they do not code for terminal action goals.

Non-transient luminance changes do not capture attention.

The processing of luminance change is a ubiquitous feature of the human visual system and provides the basis for the rapid orienting of attention to potentially important events (e.g., motion onset, object onset). However, despite its importance for attentional capture, it is not known whether a luminance change attracts attention solely because of its status as a sensory transient or can attract attention at a relatively high cognitive level. In a series of six experiments, we presented visual displays in which a single object underwent a luminance change that was either visible or obscured by a mask. A target then appeared either at the change location or elsewhere. The results showed that the luminance change attracted attention only in the visible condition. This was even observed with the largest change we could generate (> 75 cd/m(2)). These data suggest that the importance of a luminance change is only in its status as a low-level sensory transient.

Social inhibition of return.

Responses to a target stimulus can be slower when it appears in the same rather than a different location to a previous event, an effect known as inhibition of return (IOR). Recently, it has been shown that when two people alternate responses to a target, one person's responses are slower when they are directed to the same locations as their partner's previous response. The present study sought to investigate this highly novel effect, which we term social IOR (SIOR), in relation to what is known of IOR in individuals performing alone. We found that only a real conspecific can induce SIOR in another person, whereas an animated conspecific cannot. Additionally, SIOR emerges at locations to which a conspecific has been inferred to respond, even when direct observation of his/her responses is prevented. Finally, SIOR can be induced without the abrupt visual transients normally associated with the generation of IOR. These findings suggest that SIOR is the result of stronger activations of IOR mechanisms, or that it is subserved by entirely separate inhibitory processes.

Prioritization of looming and receding objects: equal slopes, different intercepts.

Franconeri and Simons (2003) reported that simulated looming objects (marked by a size increase) captured attention, whereas simulated receding objects (marked by a size decrease) did not. This finding has been challenged with the demonstration that receding objects can capture attention when they move in three-dimensional depth. In the present study, we compared the effects of objects that either loomed or receded in depth. The results of two experiments showed that whereas both motion types benefited from attentional prioritization, as judged by their search slopes, looming objects elicited shorter response times (RTs). We conclude that both motion types attract attention during search; however, the RT advantage for looming motion seems to reflect a processing enhancement that occurs outside of selection and is conferred on the basis of motion direction.

Object and spatial representations in the corner enhancement effect.

Cole, Gellatly, and Blurton have shown that targets presented adjacent to geometric corners are detected more efficiently than targets presented adjacent to straight edges. In six experiments, we examined how this corner enhancement effect is modulated by corner-of-object representations (i.e., corners that define an object's shape) and local base-level corners that occur as a result of, for instance, overlapping the straight edges of two objects. The results show that the corner phenomenon is greater for corners of object representations than for corners that do not define an object's shape. We also examined whether the corner effect persists within the contour boundaries of an object, as well as on the outside. The results showed that a spatial gradient of attention accompanies the corner effect outside the contour boundaries of an object but that processing within an object is uniform, with no corner effect occurring. We discuss these findings in relation to space-based and object-based theories of attention.

Magnetic stimulation of the left visual cortex impairs expert word recognition.

One of the hallmarks of expert reading is the ability to identify arrays of several letters quickly and in parallel. Such length-independent reading has only been found for word stimuli appearing in the right visual hemifield (RVF). With left hemifield presentation (LVF), response times increase as a function of word length. Here we investigated the comparative efficiency with which the two hemispheres are able to recognize visually presented words, as measured by word length effects. Repetitive transcranial magnetic stimulation (rTMS) of the left occipital cortex disrupted expert processing of the RVF such that a length effect was created (Experiment 1). Right occipital rTMS, on the other hand, had no such effect on RVF words and nor did it modulate the length effect already present in the LVF. Experiment 2 explored the time course of these TMS-induced effects by applying single pulses of TMS at various stimulus-onset asynchronies for the same task. We replicated the TMS-induced length effect for RVF words, but only when a single pulse was applied to the left visual cortex 80 msec after target presentation. This is the first demonstration of TMS-induced impairment producing a word length effect, and as such confirms the specialization of the left hemisphere in word recognition. It is likely that anatomical differences in the pathway linking retinal input to higher level cortical processing drive this effect.