Separate attentional resources for vision and audition

Abstract

Current models of attention, typically claim that vision and audition are limited by a common attentional resource which means that visual performance should be adversely affected by a concurrent auditory task and vice versa. Here, we test this implication by measuring auditory (pitch) and visual (contrast) thresholds in conjunction with cross-modal secondary tasks and find that no such interference occurs. Visual contrast discrimination thresholds were unaffected by a concurrent chord or pitch discrimination, and pitch-discrimination thresholds were virtually unaffected by a concurrent visual search or contrast discrimination task. However, if the dual tasks were presented within the same modality, thresholds were raised by a factor of between two (for visual discrimination) and four (for auditory discrimination). These results suggest that at least for low-level tasks such as discriminations of pitch and contrast, each sensory modality is under separate attentional control, rather than being limited by a supramodal attentional resource. This has implications for current theories of attention as well as for the use of multi-sensory media for efficient informational transmission.

Figure 1

Examples of psychometric functions for one naive observer (RA) for (a) visual contrast and (b) auditory frequency discriminations. The red symbols show the thresholds for the primary task alone, the blue symbols when performed together with the secondary task in the same modality and the green symbols when performed with the secondary task in the other modality. Chance performance was 50% (lower dashed line). The curves are best fitting cumulative Gaussians, from which thresholds were calculated (taken as the 75% correct point, indicated by the vertical dashed lines). The secondary task in the same modality clearly impeded performance, shifting the psychometric functions towards higher contrasts and frequencies, without greatly affecting their slope or general form. In this experiment, the secondary tasks were adjusted in difficulty to produce 92% correct performance when presented alone (d′=2).

Figure 2

Threshold performance for three observers (author D.A. and two naïve subjects) for visual (red bars) and auditory (green bars) discriminations all normalized by the primary-task threshold measured as a single task. A value of 1.0 (dashed line) would therefore indicate no difference in primary-task thresholds from single to dual task conditions. Values greater that 1.0 indicate worse performance in the dual task, and therefore the ‘cost’ of dividing attention. Solid bars show thresholds for dual tasks in the same modality, cross-hatching for distractor tasks were in the other modality. Diagonal cross-hatching indicates cross-modal dual tasks that were spatially co-located (indicated by ^*). The only large effects are for dual tasks in the same modality.

Figure 3

Effect of difficulty of secondary task, averaged across subjects. Stimulus detectability varied from d′=0.5 to 3, calculated individually from the psychometric functions for the secondary task performed alone (d′=1 implies 75% threshold). Clearly task difficulty has little effect, either on the within modality or between modality dual tasks. NR refers to the control condition where the secondary stimulus was displayed, but subjects were not required to respond to it.