Patrick Bourke

A General Factor Involved in Dual task Performance Decrement

Beyond specific conflicts between tasks that are obviously similar (e.g. two verbal tasks) and limits specific to speeded responses, is there a general limitation on what tasks can be done simultaneously? In two experiments, we examined dual-task combinations designed to avoid known sources of specific interference. Under these circumstances, a general factor model predicts consistency in the pattern of results. Tasks should be ordered in demands on the general factor as measured by interference with concurrent tasks; this order should be the same for any concurrent task used to measure it. This prediction was confirmed in both experiments, each involving 12 dual task combinations of four tasks. In Experiment 1, the tasks were tone discrimination, random letter generation, a manual-tactile manipulation task, and recognition memory for photographs. In Experiment 2, the first of these was replaced by an easier tone-monitoring task, and the last by a visual prototype learning task.

Memory deficit in clinical depression: processing resources and the structure of materials

Resource theory predicts that the relative memory deficit shown by depressed patients should be greater with unstructured than structured material. Previous data using semantic categories word lists supports this, but lists approximating to text have produced the opposite result. Both types of structure were studied in this experiment. The prediction from resource theory was found to hold only when comparing medium and high levels of structure, and to hold more clearly for word lists approximating to text than for semantic categories lists. When word lists of low and medium levels of structure were compared, depressed patients showed relatively greater deficit with the more structured material. Ways in which this could be accommodated in a revised version of resource theory are discussed.

Measuring Attentional Demand in Continuous Dual-task Performance

Despite its intuitive appeal, the commonly held assumption that there is some general limitation on dual-task performance has been shown to be seriously flawed (Allport 1980; Navon 1984). Central to this has been the inability to measure the attentional demands of tasks, without which there is no way to determine whether their joint demands exceed the hypothetical general limit. In the absence of such a measure, dual-task interference can always be explained by the alternative possibility that specific interference has occurred. A method is described in which the attentional demands of tasks can be measured and cross validated by the use of two scales. Two experiments are described in which a general attentional limit is found; the measurement of attentional demand is consistent across scales and can be made at a level of precision approximating that of an interval scale.

Effect of Template Complexity on Visual Search and Dual-Task Performance

Even dissimilar tasks interfere with one another when done together. We used visual search to examine the underlying cause of such interference. In many models, visual search is a process of biased competition controlled by a template describing the target to be sought. When the display is processed, matching against this template guides attention to the target. We show that increasing template complexity increased interference with a dissimilar concurrent task, story memory. This result was independent of reaction time: Increases in template complexity were associated with no increase in search time in Experiment 1 and with a decrease in search time in Experiment 2. The results show that the dual-task demands of visual search reflect the complexity of the template used in task control, and that this factor can be isolated from other sources of difficulty.

Additive effects of inhibiting attention to objects and locations in three-dimensional displays

One of the processes thought to underlie visual selection works by biasing attention away from either recently examined locations or objects. The extent of this “inhibition” is greatest when the inhibited object and the inhibited location coincide. In Experiment 1, rectangles are presented stereoscopically at different depths but at similar positions horizontally and vertically. Here, any inhibition should be based solely on a spatial code, as the objects, the rectangles are clearly separate objects. In Experiment 2, the corners of the rectangles are joined to produce a single cuboid that extends in depth space. Now inhibition based on both spatial and object codes should be seen because even when on different depth planes the cue and target are associated with the same object. Consistent with our understanding of the additive effects of inhibition of space and object codes, the extent of inhibition in the second study is almost double that of the first. The results further suggest that space-based inhibition operates within a two-dimensional representation while object-based inhibition utilizes a three-dimensional representation.

Attending at a Low Intensity Increases Impulsivity in an Auditory Sustained Attention to Response Task

Why attention lapses during prolonged tasks is debated, specifically whether errors are a consequence of under-arousal or exerted effort. To explore this, we investigated whether increased impulsivity is associated with effortful processing by modifying the demand of a task by presenting it at a quiet intensity. Here, we consider whether attending at low but detectable levels affects impulsivity in a population with intact hearing. A modification of the Sustained Attention to Response Task was used with auditory stimuli at two levels: the participants’ personal “lowest detectable” level and a “normal speaking” level. At the quiet intensity, we found that more impulsive responses were made compared with listening at a normal speaking level. These errors were not due to a failure in discrimination. The findings suggest an increase in processing time for auditory stimuli at low levels that exceeds the time needed to interrupt a planned habitual motor response. This leads to a more impulsive and erroneous response style. These findings have important implications for understanding the nature of impulsivity in relation to effortful processing. They may explain why a high proportion of individuals with hearing loss are also diagnosed with Attention Deficit Hyperactivity Disorder.

Influence of hand position on the near effect in 3-D attention

Voluntary reorienting of attention in real depth situations is characterized by an attentional bias to locations nearer the viewer once attention is deployed to a spatially cued object in depth. Previously, this effect (initially referred to as the near effect) was attributed to access of a 3-D viewer-centered spatial representation for guiding attention in 3-D space. The aim of this study was to investigate whether the near effect could have been associated with the position of the response hand, which was always near the viewer in previous studies that investigated endogenous attentional shifts in real depth. In Experiment 1, the response hand was placed at either the near or far target depth in a depth-cuing task. Placing the response hand at the far target depth abolished the near effect, but failed to bias spatial attention to the far location. Experiment 2 showed that the response hand effect was not modulated by the presence of an additional (passive) hand, whereas Experiment 3 confirmed that attentional prioritization of the passive hand was not masked by the influence of the responding hand on spatial attention in Experiment 2. The pattern of results is most consistent with the idea that response preparation can modulate spatial attention within a 3-D viewer-centered spatial representation.

Hearing without listening: attending to a quiet audiobook

Careful systematic tests of hearing ability may miss the cognitive consequences of sub-optimal hearing when listening in the real world. In Experiment 1, sub-optimal hearing is simulated by presenting an audiobook at a quiet but discriminable level over 50 min. Recall of facts, words and inferences are assessed and performance compared to another group at a comfortable listening volume. At the quiet intensity, participants are able to detect, discriminate and identify spoken words but do so at a cost to sequential accuracy and fact recall when attention must be sustained over time. To exclude other interpretations, the effects are studied in Experiment 2 by comparing recall to the same sentences presented in isolation. Here, the differences disappear. The results demonstrate that the cognitive consequences of listening at low volume arise when sustained attention is demanded over time.