Contrasting Predictions of Low- and High-Threshold Models for the Detection of Changing Visual Features

Attribute Amnesia in the Auditory Domain

Individuals are often unable to report an attribute of an object to which they recently attended, if they expected to report a different attribute, a phenomenon known as attribute amnesia (AA). To date, all AA studies have occurred in the visual domain. The purpose of this study was to explore the boundary conditions of AA by testing if AA also occurs in the auditory domain and, if so, for which attributes. It was found that AA was present when reporting the location (p = .003) and the number of tones (p < .001) of an auditory stimulus, but not when reporting its pitch (p = .383). These findings can be understood in terms of the organisation of the primary cortical areas and help explain the differences between visual working memory and auditory working memory.

Concurrent evaluation of independently cued features during perceptual decisions and saccadic targeting in visual search

Simultaneous search for one of two targets is slower and less accurate than search for a single target. Within the Signal Detection Theoretic (SDT) framework, this can be attributed to the division of resources during the comparison of visual input against independently cued targets. The current study used one or two cues to elicit single- and dual-target searches for orientation targets among similar and dissimilar distractors. In Experiment 1, the accuracy of target discrimination in brief displays was compared at setsizes of 1, 2 and 4. Results revealed a reduction in accuracy that scaled with the product of set size and the number of cued targets. In Experiment 2, the accuracy and latency of observers’ saccadic targeting were compared. Fixations on single-target searches were highly selective towards the target. On dual-target searches, the requirement to detect one of two targets produced a significant reduction in target fixations and equivalent rates of fixations to distractors with opposite orientations. For most observers, the dual-target cost was predicted by an SDT model that simulated increases in decision-noise and the distribution of capacity-limited resources during the comparison of selected input against independently cued targets. For others, search accuracy was consistent with a single-item limit on perceptual decisions and saccadic targeting during search. These findings support a flexible account of the dual-target cost based on different strategies to resolve competition between independently cued targets.

Attentional control via parallel target-templates in dual-target search

Simultaneous search for two targets has been shown to be slower and less accurate than independent searches for the same two targets. Recent research suggests this 'dual-target cost' may be attributable to a limit in the number of target-templates than can guide search at any one time. The current study investigated this possibility by comparing behavioural responses during single- and dual-target searches for targets defined by their orientation. The results revealed an increase in reaction times for dual- compared to single-target searches that was largely independent of the number of items in the display. Response accuracy also decreased on dual- compared to single-target searches: dual-target accuracy was higher than predicted by a model restricting search guidance to a single target-template and lower than predicted by a model simulating two independent single-target searches. These results are consistent with a parallel model of dual-target search in which attentional control is exerted by more than one target-template at a time. The requirement to maintain two target-templates simultaneously, however, appears to impose a reduction in the specificity of the memory representation that guides search for each target.

Detecting unidentified changes

Does becoming aware of a change to a purely visual stimulus necessarily cause the observer to be able to identify or localise the change or can change detection occur in the absence of identification or localisation? Several theories of visual awareness stress that we are aware of more than just the few objects to which we attend. In particular, it is clear that to some extent we are also aware of the global properties of the scene, such as the mean luminance or the distribution of spatial frequencies. It follows that we may be able to detect a change to a visual scene by detecting a change to one or more of these global properties. However, detecting a change to global property may not supply us with enough information to accurately identify or localise which object in the scene has been changed. Thus, it may be possible to reliably detect the occurrence of changes without being able to identify or localise what has changed. Previous attempts to show that this can occur with natural images have produced mixed results. Here we use a novel analysis technique to provide additional evidence that changes can be detected in natural images without also being identified or localised. It is likely that this occurs by the observers monitoring the global properties of the scene.