Conscious awareness modulates processing speed in the redundant signal effect

Evidence for the influence of unaware signals on behaviour has been reported in both patient groups and healthy observers using the Redundant Signal Effect (RSE). The RSE refers to faster manual reaction times to the onset of multiple simultaneously presented target than those to a single stimulus. These findings are robust and apply to unimodal and multi-modal sensory inputs. A number of studies on neurologically impaired cases have demonstrated that RSE can be found even in the absence of conscious experience of the redundant signals. Here, we investigated behavioural changes associated with awareness in healthy observers by using Continuous Flash Suppression to render observers unaware of redundant targets. Across three experiments, we found an association between reaction times to the onset of a consciously perceived target and the reported level of visual awareness of the redundant target, with higher awareness being associated with faster reaction times. However, in the absence of any awareness of the redundant target, we found no evidence for speeded reaction times and even weak evidence for an inhibitory effect (slowing down of reaction times) on response to the seen target. These findings reveal marked differences between healthy observers and blindsight patients in how aware and unaware information from different locations is integrated in the RSE.

Cross-modal perceptual enhancement of unisensory targets is uni-directional and does not affect temporal expectations

Previous studies demonstrated that redundant target stimuli can enhance performance due to multisensory interplay and interactively facilitate performance enhancements due to temporal expectations (TE; faster and accurate reactions to temporally expected targets). Here we tested whether other types of multisensory interactions – i.e. interactions evoked by temporally flanking irrelevant stimuli – can result in similar performance patterns and boost not only unisensory target perception (multi-vs. unisensory sequences) but also unisensory temporal expectations (expected vs. unexpected). To test our hypothesis, we presented sequences of 12 stimuli (10 Hz) which either consisted of auditory (A), visual (V) or alternating auditory-visual stimuli (e.g. A-V-A-V-…) with either auditory (AV(A)) or visual (AV(V)) targets. Participants had to discriminate target frequency which was unpredictable by temporal regularities (expected vs. unexpected target positions) and by stimulation sequence (A, V, AV(A), AV(V)). Moreover, we ran two experiments in which we presented redundant multisensory targets and manipulated the speed of the stimulation sequence (10 vs. 15 Hz stimulus trains) to control whether the results of Experiment 1 depended on sequence speed. Performance for unisensory targets was affected by temporally flanking distractors, with multisensory interactions selectively improving unisensory visual target perception. Yet, only redundant multisensory targets reliably affected TEs. Together, these results indicate that cross-modal facilitation of unisensory target perception in fast stimulus streams is uni-directional, but also differs from multisensory interactions evoked by redundant targets; more specifically, it appears to be context-dependent (task, design etc.) whether unisensory stimulation (unlike redundant target stimulation) allows for the generation of temporal expectations.

Dual-Task Redundant-Target Processing: The Case of the Limited Capacity Parallel Model

We examined the effect of a central tracking task on visual target processing efficiency in a combined target detection / manual tracking paradigm. Participants performed a redundant-target task by itself, and concurrently with the tracking task. A measure of workload capacity gauged target processing efficiency. Processing was less efficient than predicted by a standard parallel race model under both levels of task load. However, data suggested no difference in processing efficiency between the single-and dual-task conditions. Our findings provide further evidence that processing capacity for peripheral visual targets is consistently limited but robust against changes to concurrent task load.

Unchanging Capacity

Complex workspaces often require operators to divide attention between information within the visual periphery and a visual central task. For an air traffic controller, for example, monitoring complex displays while also watching for potential hazards is essential for avoiding aircraft collisions. In such environments, fast and accurate detection of peripheral events may be critical for safe performance. Presenting targets redundantly offers a potential way of speeding up target detection (Little, Eidels, Fific, & Wang, 2015; Townsend & Eidels, 2011). It remains unclear, however, whether redundant-target processing remains efficient with a concurrent central task. A series of experiments examined the effects of dual-tasking on peripheral redundant-target processing, either between- (Experiments 1a & 1b) or within-participants (Experiment 4). Furthermore, Experiments 2 and 3 manipulated target-distractor discriminability and distractor presence to examine the effects of target salience on dual-task processing efficiency. One hundred and one undergraduate students ( N =20 in each of Experiments 1a to 3; N = 21 in Experiment 4) performed a redundant-target task either by itself (Experiment 1a) or whilst performing a manual tracking task (Experiments 1b-4). The tracking task required participants to maneuver a joystick using both hands to align a cursor with a moving red target. The detection task required participants to press a joystick button bimanually whenever a target appeared at a location in the peripheral visual field. Experiments 1a, 1b, and Experiment 4 employed “T” as the target item and “L” as distractor items that appeared randomly rotated in 90° steps. In Experiment 2, target salience was increased by employing “X” as the target item and “O” for the distractor items. Experiment 3 tested peripheral target processing in the absence of distractors; hence, only the target item “T” was employed. Processing efficiency in the target-detection task was calculated using measures of resiliency (Little et al., 2015) or workload capacity (Townsend & Eidels, 2011). In all five experiments, processing of redundant targets was less efficient than predicted by a standard parallel race model (Raab, 1962; Townsend & Eidels, 2011). Surprisingly, processing efficiency differed negligibly between the single and dual-task conditions. Capacity may be protected from task-load effects due to separate information-processing resource pools within the central and peripheral visual fields (Wickens, 2002). Neither increasing the discriminability between targets and distractors, nor removing distractors entirely, had any effect on redundant-target processing efficiency. Results suggest target processing in the visual periphery is capacity-limited, but that processing efficiency is robust against changes to concurrent task load or target salience.