Jason J. Braithwaite

Seeing It Their Way: Evidence for Rapid and Involuntary Computation of What Other People See.

In a series of three visual perspective-taking experiments, we asked adult participants to judge their own or someone elses visual perspective in situations where both perspectives were either the same or different. We found that participants could not easily ignore what someone else saw when making self-perspective judgments. This was observed even when participants were only required to take their own perspective within the same block of trials (Experiment 2) or even within the entire experiment (Experiment 3), i.e. under conditions which gave participants a clear opportunity to adopt a strategy of ignoring the other persons irrelevant perspective. Under some circumstances, participants were also more efficient at judging the other persons perspective than at judging their own perspective. Collectively, these results suggest that adults make use of rapid and efficient processes to compute what other people can see.

Inhibition and anticipation in visual search: Evidence from effects of color foreknowledge on preview search

We present four experiments in which we examined the effects of color mixing andprior target color knowledge on preview search (Watson & Humphreys, 1997). The task was to detect a target letter (an N or a Z) that appeared along with other new letters, when old distractors remained in the visual field. In some conditions, participants were told the target’s color; in others, they were not. Foreknowledge of the target’s color produced large improvements in search for both baseline and preview presentations (Experiment 1). For preview presentations, the magnitude of this effect was reduced if the target shared its color with a single colored set of previewed letters (Experiment 2). Removing this similarity across the displays greatly improved search efficiency (Experiment 3). In Experiment 4, we assessed and rejected the proposal that the effects reflected the probability that the target was carried by a particular color. We discuss the results in terms of separate effects of (1) inhibitory carryover from a preview color group and (2) an anticipatory set for a known target color.

Color-based grouping and inhibition in visual search : evidence from a probe-detection analysis of preview search

In four experiments, we examined selection processes in visual search using a probe detection task to measure the allocation of attention. Under preview search conditions, probes were harder to detect on old relative to new distractors (Experiment 1). This cannot be attributed solely to low-level sensory factors (Experiment 2). In addition, probe detection was sensitive to color-based grouping of old distractors and to color similarity between old distractors (Experiments 3 and 4). These effects were dissociated when the color of the old distractors changed but probe detection effects remained. Collectively, the data indicate both group-based suppression of distractors and the separate inhibition of distractor features in search.

Cognitive correlates of the spontaneous out-of-body experience (OBE) in the psychologically normal population : evidence for an increased role of temporal-lobe instability, body-distortion processing, and impairments in own-body transformations

Recent findings from studies of epileptic patients and schizotypes have suggested that disruptions in multi-sensory integration processes may underlie a predisposition to report out-of-body experiences (OBEs: Blanke et al., 2004; Mohr et al., 2006). It has been argued that these disruptions lead to a breakdown in own-body processing and embodiment. Here we present two studies which provide the first investigation of predisposition to OBEs in the normal population as measured primarily by the recently devised Cardiff anomalous perception scale (CAPS; Bell et al., 2006). The Launay-Slade Hallucination scale (LSHS) was also employed to provide a measure of general hallucination proneness. In Study 1, 63 University students participated in the study, 17 of whom (26%) claimed to have experienced at least one OBE in their lifetime. OBEers reported significantly more perceptually anomalies (elevated CAPS scores) but these were primarily associated with specific measures of temporal-lobe instability and body-distortion processing. Study 2 demonstrated that OBEers and those scoring high on measures of temporal-lobe instability/body-distortion processing were significantly impaired, relative to controls, at a task requiring mental own-body transformations (OBTs) (Blanke et al., 2005). These results extend the findings from epileptic patient studies to the psychologically normal population and are consistent with there being a disruption in temporal-lobe and body-based processing underlying OBE-type experiences.

Color grouping in space and time: evidence from negative color-based carryover effects in preview search.

Five experiments addressed the role of color grouping in preview search (D. G. Watson & G. W. Humphreys, 1997). Experiment 1 used opposite color ratios of distractors in preview and second search displays, creating equal numbers of distractors in each color group in the final display. There was selective slowing for new targets carrying the majority color of the old items. This effect held when there was no bias in the preview and only the second search set had an uneven color ratio (Experiment 2). In Experiment 3, participants had foreknowledge of the target color, and effects were shown over and above those due to color biases. Experiment 4 demonstrated negative color carryover even when previews changed color. Experiment 5 showed reduced color carryover effects when previews were presented more briefly. Collectively, the results provide evidence for inhibitory carryover effects in preview search based on feature grouping.

The preview search task: Evidence for visual marking.

A series of experiments are reviewed providing evidence for the idea that when new visual objects are prioritized, old objects are inhibited by a top-down controlled suppression mechanism—a process referred to as visual marking. Evidence for the top-down aspect of visual marking is presented, by showing that new object prioritization, as measured in the preview paradigm, depends on task settings and available attentional resources. Evidence for the inhibitory aspect is presented, by showing that selection of new items is impaired when these items share features with the old items. Such negative carryover effects occur within as well as between trials. Alternative accounts and the evidence for them is discussed. It is concluded that the various accounts are not mutually exclusive and that the data is best explained by a combination of mechanisms.

Is it impossible to inhibit isoluminant items, or does it simply take longer? Evidence from preview search

Visual search can be facilitated when participants receive a preview of half the distractors (the preview benefit in search; Watson & Humphreys, 1997). Donk and Theeuwes (2001) have argued that preview-based benefits are abolished if the display items are isoluminant to a background. This is consistent with the preview benefit being due to onset capture by the new stimuli. In contrast, the present experiments challenge this suggestion and show that preview benefits can occur under isoluminant conditions, providing that they are given enough time to occur. In Experiment 1, we showed that a preview benefit can occur even with isoluminant stimuli, provided that the old items are previewed for a sufficient time. In Experiment 2, we tested and rejected the idea that this advantage is due to low-level sensory fatigue for the preview stimuli. These findings indicate that the preview effect is not caused solely by onset capture. nt]mis|This rese was supported by a British Academy postdoctoral fellowship awarded to the first author and an MRC grant to the fourth author.

Fast Color Grouping and Slow Color Inhibition: Evidence for Distinct Temporal Windows for Separate Processes in Preview Search.

The authors report 4 experiments that examined color grouping and negative carryover effects in preview search via a probe detection task (J. J. Braithwaite, G. W. Humphreys, & J. Hodsoll, 2003). In Experiment 1, there was evidence of a negative color carryover from the preview to new items, using both search and probe detection measures. There was also a negative bias against probes on old items that carried the majority color in the preview. With a short preview duration (150 ms) carryover effects to new items were greatly reduced, but probe detection remained biased against the majority color in the old items. Experiments 2 and 4 showed that the color bias effects on old items could be reduced when these items had to be prioritized relative to being ignored. Experiment 3 tested and rejected the idea that variations in the probability of whether minority or majority colors were probed were crucial. These results show that the time course of color carryover effects can be separated from effects of early color grouping in the preview display: Color grouping is fast, and inhibitory color carryover effects are slow.

Revisiting preview search at isoluminance: new onsets are not necessary for the preview advantage.

It has been argued that search performance underpreview conditions relies on automatic capture by luminance onsets (Donk & Theeuwes, 2001). We present three experiments in which preview search was examined with both isoluminant and nonisoluminant items (e.g., as defined by luminance onsets). Experiment 1 provided evidence against the automatic capture of attention by onsets. Search benefited when onset previews were followed by new onset stimuli, as compared with a full-set baseline matched for the number of new onsets but in which half the distractors appeared simultaneously at isoluminance. Furthermore, both Experiments 1 and 2 established a preview advantage when isoluminant targets followed onset previews, when compared with appropriate full-set baselines. Experiment 3 replicated this result, while showing that the preview benefit was disrupted by dual-task interference. The data indicate that new onsets are not necessary to generate a preview advantage in search. We discuss the data in terms of search’s benefiting from active inhibition of old onset-defined stimuli.

Dissociating the effects of similarity, salience, and top-down processes in search for linearly separable size targets

In two experiments, we explored the role of foreknowledge on visual search for targets defined along the size continuum. Targets were of large, medium, or small size and of high or low similarity relative to the distractors. In Experiment 1, we compared search for known and unknown singleton feature targets as a function of their size and similarity to the distractors. When distractor similarity was high, target foreknowledge benefited targets at the end of the size continuum (i.e., large and small) relatively more than targets of medium size. In Experiment 2, participants were given foreknowledge of what the target was not. The beneficial effect of foreknowledge for endpoint targets was reduced. The data indicate the role of top-down templates in search, which can be “tuned” more effectively for targets at the ends of feature dimensions.