Cross-modal attentional deficits in processing tactile stimulation

In order to substantiate recent theorization on the possible links between the causes of the attentional blink and the psychological refractory period phenomena (e.g., Jolicoeur, 1999a), four experiments are reported in which two target stimuli, T₁ and T₂, were presented in different modalities at varying stimulus onset asynchronies (SOAs), with each stimulus being associated with a distinct task, Task₁ and Task₂. In Experiment 1, T₁ was a tone, and Task₁ was a speeded vocal response based on pitch. T₂ was a brief press applied to either of two distal fingerpads, and Task₂ was a speeded manual response based on tactile stimulus location. In Experiment 2, the same T₁ as that used in Experiment 1 was presented, and in Task₁ the subject either made a speeded vocal response based on pitch or ignored T₁. T₂ was a masked tactile stimulation, and Task₂ was an unspeeded manual discrimination of the tactile stimulation location. This Task₂ was maintained in Experiments 3 and 4. The auditory T₁ was replaced with a white digit embedded in a rapid serial visualization presentation of a stream of black letters, and in Task₁ the subject either made an unspeeded decision based on T₁ identity or ignored T₁. In all the experiments, the results showed an SOA-locked impairment in Task₂. As SOA was decreased, reaction times in the speeded Task₂ of Experiment 1 increased, and accuracy in the unspeeded Task₂ of Experiments 2–4 decreased. The SOA-locked impairment was almost eliminated when T₁ could be ignored or was absent. The results are discussed in terms of central processing limitations as the cause of such effects.     

The control of stimulus-driven saccades is subject not to central, but to visual attention limitations

In three experiments, we investigated whether the control of reflexive saccades is subject to central attention limitations. In a dual-task procedure, Task 1 required either unspeeded reporting or ignoring of briefly presented masked stimuli, whereas Task 2 required a speeded saccade toward a visual target. The stimulus onset asynchrony (SOA) between the two tasks was varied. In Experiments 1 and 2, the Task 1 stimulus was one or three letters, and we asked how saccade target selection is influenced by the number of items. We found (1) longer saccade latencies at short than at long SOAs in the report condition, (2) a substantially larger latency increase for three letters than for one letter, and (3) a latency difference between SOAs in the ignore condition. Broadly, these results match the central interference theory. However, in Experiment 3, an auditory stimulus was used as the Task 1 stimulus, to test whether the interference effects in Experiments 1 and 2 were due to visual instead of central interference. Although there was a small saccade latency increase from short to long SOAs, this difference did not increase from the ignore to the report condition. To explain visual interference effects between letter encoding and stimulus-driven saccade control, we propose an extended theory of visual attention.     

Holding a manual response sequence in memory can disrupt vocal responses that share semantic features with the manual response

Holding an action plan in memory for later execution can delay execution of another action if the actions share a similar (compatible) feature. This compatibility interference (CI) occurs for actions that share the same response modality (e.g., manual response). We investigated whether CI can generalize to actions that utilize different response modalities (manual and vocal). In three experiments, participants planned and withheld a sequence of key-presses with the left- or right-hand based on the visual identity of the first stimulus, and then immediately executed a speeded, vocal response (‘left’ or ‘right’) to a second visual stimulus. The vocal response was based on discriminating stimulus color (Experiment 1), reading a written word (Experiment 2), or reporting the antonym of a written word (Experiment 3). Results showed that CI occurred when the manual response hand (e.g., left) was compatible with the identity of the vocal response (e.g., ‘left’) in Experiment 1 and 3, but not in Experiment 2. This suggests that partial overlap of semantic codes is sufficient to obtain CI unless the intervening action can be accessed automatically (Experiment 2). These findings are consistent with the code occupation hypothesis and the general framework of the theory of event coding (Behav Brain Sci 24:849–878, 2001a; Behav Brain Sci 24:910–937, 2001b).     

Stimulus and response priming in rapid serial visual presentation: evidence for a dissociation

Two experiments investigated the capacity demands of stimulus and response priming in a rapid serial visual presentation (RSVP) task. Three targets were presented in a stream of visual symbols: The first two (T1 and T2) required an unspeeded manual response at the end of the trial, but the third (T3) called for an immediate,speeded manual response. T2 and T3 either were identical (fully compatible), required the same response (response compatible), or required different responses (incompatible). Priming in the fully compatible condition depended strongly on successful identification of the priming stimulus, whereas response-based priming was observed regardless of whether the prime could be reported or not. These findings suggest that stimulus coding and response coding are automatic processes, unaffected by attentional capacity constraints, followed by capacity-limited stimulus consolidation and response selection. Moreover, even though response codes are activated automatically upon stimulus processing, both types of codes act, and affect behavior, independently.     

Can practice overcome age-related differences in the psychological refractory period effect?

Can dual-task practice remove age-related differences in the psychological refractory period (PRP) effect? To answer this question, younger and older individuals practiced 7 blocks of a PRP design, in which Task 1 (T1) required a vocal response to an auditory stimulus and Task 2 (T2) required a manual response to a visual stimulus (Experiment 1). The results showed that practice did not reduce, but rather increased, age-related differences in PRP interference. Using the trained individuals, the introduction of a less complex new T1 (Experiment 2) or a less complex new T2 (Experiment 3) with the task previously practiced reduced the PRP interference but only in older adults. The authors propose that older adults suffer from a large task-switch cost that is more sensitive to task complexity than to the amount of practice.     

Can practice eliminate the psychological refractory period effect?

Can people learn to perform two tasks at the same time without interference? To answer this question, the authors trained 6 participants for 36 sessions in a Psychological Refractory Period (PRP) experiment, where Task 1 required a speeded vocal response to an auditory stimulus and Task 2 required a speeded manual response to a visual stimulus. The large PRP effect found initially (353 ms in Session 1) shrank to only about 40 ms over the course of practice, disappearing entirely for 1 of the 6 participants. This reduction in the PRP effect with practice is considerably larger than has been previously reported. The obtained pattern of factor interactions between stimulus onset asynchrony and each of three task difficulty manipulations (Task 1 judgment difficulty, Task 2 stimulus contrast, and Task 2 mapping compatibility) supports a postponement (bottleneck) account of dual-task interference, both before and after practice.     

Cued shifts of attention and memory encoding in partial report: A dual-task approach

This study explores how cued shifts of visual attention and rapid encoding of visual information relate to limited-capacity processing mechanisms. Three experiments were conducted placing a partial-report task within a dual-task paradigm. Experiments 1 and 2 involved a simple speeded visual discrimination (Task 1) and then an unspeeded partial-report task (Task 2). Generally, Task 2 accuracy declined as the temporal overlap between the two tasks increased. In addition, in Experiment 1, varying the number of items in the partial-report display had an effect on performance regardless of overlap. In contrast, in Experiment 2, varying the type of probe had an effect only at long task overlap. The generality of the interference effect was tested in Experiment 3 using an auditory discrimination as Task 1. Again, Task 2 accuracy declined as the temporal overlap between the two tasks increased. In all cases, the observed interference had the properties of a processing bottleneck. It is argued that encoding information into memory and response selection for the first task both require general-purpose processing. The results are discussed in terms of the functional relationship between attention and memory.     

Does perceptual analysis continue during selection and production of a speeded response?

This study asked whether perceptual analysis of a stimulus can continue while a response to this stimulus is being generated. In Experiment 1, subjects rapidly named a word that was visually degraded with superimposed pixels. Near the time of response, degradation was removed for a short time and then followed by a mask. Subjects then made a second, unspeeded judgment about the identity of the word. Unspeeded judgments were more accurate, showing that the degradation-free stimulus exposure was processed. In Experiment 2, the task was the same, but the degradation was gradually faded out for an individually adjusted duration. Comparison of unspeeded-response accuracy on trials with and without a speeded response showed that stimulus analysis continued at full efficiency during speeded-response generation. The results support conclusions of Rabbitt and Vyas (1981) that perceptual analysis continues during response stages. This form of continuous processing does not necessarily contradict discrete stage models of human information processing, however.     

The attentional blink is susceptible to concurrent perceptual processing demands

In a rapid serial visual presentation stream processing of a first target (T1) impairs detection or identification of a second target (T2) that appears within 500 ms after T1. This effect characterizes the so-called attentional blink (AB). To evaluate contemporary information-processing accounts of the AB phenomenon in terms of the underlying processing mechanisms the present study examined the potential influence of Task 1 difficulty on the AB effect. To this end, T1 contrast and T1 response requirements were systematically varied across four experiments. Experiment 1 ruled out a mere sensory basis of the contrast manipulation on T2 performance. When only T2 had to be reported (Experiment 2) an AB effect occurred that was slightly modulated by T1 contrast. When report of both T1 and T2 was required in a standard AB task (Experiment 3), the magnitude of the AB depended to a larger extent on stimulus contrast, and it increased further when speeded T1 choice responses were additionally required (Experiment 4). On the basis of the present impact of Task 1 difficulty on the AB effect we conclude that processing limitations cause the AB phenomenon. We discuss such limitations in terms of perceptual (T1 consolidation) and central (response selection) bottleneck processes.     

Evidence for the integration of audiovisual emotional information at the perceptual level of processing

The present aim was to investigate how emotional expressions presented on an unattended channel affect the recognition of the attended emotional expressions. In Experiments 1 and 2, facial and vocal expressions were simultaneously presented as stimulus combinations. The emotions (happiness, anger, or emotional neutrality) expressed by the face and voice were either congruent or incongruent. Subjects were asked to attend either to the visual (Experiment 1) or auditory (Experiment 2) channel and recognise the emotional expression. The result showed that the ignored emotional expressions significantly affected the processing of attended signals as measured by recognition accuracy and response speed. In general, attended signals were recognised more accurately and faster in congruent than in incongruent combinations. In Experiment 3, possibility for a perceptual-level integration was eliminated by presenting the response-relevant and response-irrelevant signals separated in time. In this situation, emotional information presented on the nonattended channel ceased to affect the processing of emotional signals on the attended channel. The present results are interpreted to provide evidence for the view that facial and vocal emotional signals are integrated at the perceptual level of information processing and not at the later response-selection stages.     

Do response modality effects support multiprocessor models of divided attention?

Some studies have suggested that dual-task interference is greatly reduced when tasks requiring very different types of responses (e.g., manual and vocal) are combined. However, in those studies, the order of stimuli varied unpredictably. In Experiments 1 and 2, variable stimulus order greatly inflated interference between two manual tasks, whereas interference between a manual and a vocal task was only slightly exacerbated. However, central interference (the psychological refractory period) persisted even with the manual/vocal combination. Selection of 2 manual responses with unknown stimulus order may require a special strategy to preclude intertask intrusion errors. Experiment 3 demonstrated that such errors could be provoked with speed stress. Together, these results reconcile response modality effects with the response selection bottleneck model for dual-task interference (once it is suitably amended).     

Selection and consolidation of objects and actions

Response selection bottleneck models attribute performance costs under dual-task conditions to the human inability to select more than one response at a time. Consistent with this claim Pashler (1991) found that carrying out a speeded manual choice reaction time (RT) task does not impair the unspeeded report of a cued visual target from a masked display. In contrast, Jolicoeur and DellAcqua (1999, Experiment 2) observed pronounced interference between a speeded manual choice RT task and the unspeeded report of a small number of visually presented letters, a finding they attributed to resource sharing between response selection and stimulus consolidation. We demonstrate that comparable costs are obtained with the same task combination used by Pashler (1991) if only task order is reversed—a manipulation that is likely to increase the necessity of consolidating the target stimulus into working memory. We also found that these costs are not diminished if the location of the target to be reported is cued in advance (reducing demands on spatial focusing) and that they do not vary with the number of target features to be reported. These findings support a consolidation account of costs in dual-task performance.     

Separate and shared sources of dual-task cost in stimulus identification and response selection

There is often strong interference if a second target stimulus (T2) is presented before processing of a prior target stimulus (T1) is complete. In the "Psychological Refractory Period" (PRP) paradigm, responses are speeded and interference manifests as increased response time for T2. In the "Attentional Blink" (AB) paradigm, stimuli are masked and responses unspeeded; interference manifests as reduced T2 accuracy. While different causes have usually been considered for PRP and AB phenomena, recent evidence has supported a unified account based on a single, shared restriction on concurrent processing. Here we show that a full assessment of separate and shared resource limitations requires direct comparison of hybrid PRP/AB trials with corresponding pure PRP and AB cases. Randomizing trial types in such a comparison also brings substantial benefit in addressing possible changes in task preparation or readiness. The data from two such experiments--combining speeded auditory (SA) and unspeeded visual (UV) task events--provide clear evidence for both separate and shared resource limitations. Often interference is strongest for T1 and T2 events of the same type, reflecting predominantly different limitations in SA and UV processing. With modest increases in demand, however, interference between different event types can also be made arbitrarily large, reflecting arbitrarily important shared limitations. For even such simple tasks as these, T--T2 interference reflects a combination of relatively local and relatively global sources.     

Cross-modal links in exogenous covert spatial orienting between touch, audition, and vision

Three experiments investigated cross-modal links between touch, audition, and vision in the control of covert exogenous orienting. In the first two experiments, participants made speeded discrimination responses (continuous vs. pulsed) for tactile targets presented randomly to the index finger of either hand. Targets were preceded at a variable stimulus onset asynchrony (150,200, or 300 msec) by a spatially uninformative cue that was either auditory (Experiment 1) or visual (Experiment 2) on the same or opposite side as the tactile target. Tactile discriminations were more rapid and accurate when cue and target occurred on the same side, revealing cross-modal covert orienting. In Experiment 3, spatially uninformative tactile cues were presented prior to randomly intermingled auditory and visual targets requiring an elevation discrimination response (up vs. down). Responses were significantly faster for targets in both modalities when presented ipsilateral to the tactile cue. These findings demonstrate that the peripheral presentation of spatially uninforrnative auditory and visual cues produces cross-modal orienting that affects touch, and that tactile cues can also produce cross-modal covert orienting that affects audition and vision.     

On the nonautomaticity of visual word processing: electrophysiological evidence that word processing requires central attention

The present study used event-related potentials (ERPs) to determine the degree to which people can process words while devoting central attention to another task. Experiments 1-4 measured the N400 effect, which is sensitive to the degree of mismatch between a word and the current semantic context. Experiment 5 measured the P3 difference between low- and high-frequency words. Because these effects can occur only if a word has been identified, both ERP components index word processing. The authors found that the N400 effect (Experiments 1, 3, and 4) and the P3 difference (Experiment 5) were strongly attenuated for Task 2 words presented nearly simultaneously with Task 1. No such attenuation was found when the Task 1 stimulus was presented but required no response (Experiment 2). Strong attenuation was also evident when the Task 2 word was presented before the Task 1 stimulus (Experiment 4), suggesting that central resources are not allocated to stimuli first-come, first-served but rather are strategically locked to Task 1. The authors conclude that visual word processing is not fully automatic but rather requires access to limited central attentional resources.     

Attentional blink for color

Colored letters were presented by means of rapid serial visual presentation (RSVP). Two letters (T1 and T2) were targets that required a speeded (T1) or delayed (T2) response. T1 was shown on half of the trials. Two tasks were performed in the experimental conditions. Task 1 required a discrimination between 2 letters (when T1 was shown) or an indication that T1 was absent. In Experiment 1, Task 2 was to detect the presence of a unique color in the RSVP stream (e.g., green in a stream of alternating red and gray). In Experiment 2, Task 2 was to report the color of the first colored letter to appear in the RSVP stream. The lag between T1 and T2 in the RSVP stream was manipulated. Accuracy of color reports in Task 2 was poor at shorter lags and improved as the lag was lengthened in both experiments, demonstrating an attentional blink for chromatic information. Theoretical implications of the results are discussed.     

The Simon effect in vocal responses

The Simon effect refers to the finding that faster responses are made to non-spatial stimulus features (e.g., color) when the positions of stimulus and response correspond than when they do not correspond. The usual explanation is that a spatial stimulus code automatically activates a corresponding spatial response code. Recently, however, the Simon effect has also been observed in vocal responses. The present study investigated the properties of Simon effects in the vocal modality. Experiment 1 compared horizontal and vertical Simon effects in vocal responses and found similar patterns of sequential modulations, but different time-courses. Yet the observed results are similar to those described in the literature for manual Simon effects. Experiments 2 and 3 used a dual-task procedure to investigate the impact of manual response codes on the encoding of irrelevant location and the initiation of vocal responses, respectively. Results suggest close links between manual response codes and conceptually corresponding vocal response codes.     

Generalizing attentional control across dimensions and tasks: Evidence from transfer of proportion-congruent effects

Three experiments investigated transfer of list-wide proportion congruent (LWPC) effects from a set of congruent and incongruent items with different frequency (inducer task) to a set of congruent and incongruent items with equal frequency (diagnostic task). Experiments 1 and 2 mixed items from horizontal and vertical Simon tasks. Tasks always involved different stimuli that varied on the same dimension (colour) in Experiment 1 and on different dimensions (colour, shape) in Experiment 2. Experiment 3 mixed trials from a manual Simon task with trials from a vocal Stroop task, with colour being the relevant stimulus in both tasks. There were two major results. First, we observed transfer of LWPC effects in Experiments 1 and 3, when tasks shared the relevant dimension, but not in Experiment 2. Second, sequential modulations of congruency effects transferred in Experiment 1 only. Hence, the different transfer patterns suggest that LWPC effects and sequential modulations arise from different mechanisms. Moreover, the observation of transfer supports an account of LWPC effects in terms of list-wide cognitive control, while being at odds with accounts in terms of stimulus–response (contingency) learning and item-specific control.     

Feature and conjunction processing in the auditory modality

In five experiments, participants made speeded target/nontarget classification responses to singly presented auditory stimuli. Stimuli were defined via vocal identity and location in Experiments 1 and 2 and frequency and location in the remaining experiments. Performance was examined in two conditions inspired by visual search: In the feature condition, responses were based on the detection of unique stimulus features; in the conjunction condition, unique combinations of features were critical. Experiment 1 showed a conjunction benefit, since classifications were faster in the conjunction condition than in the feature condition. Potential confounds were eliminated in Experiments 2 and 3, which resulted in the observation of conjunction costs. In Experiments 4 and 5, we examined, respectively, whether the cost could be explained in terms of differences in interstimulus similarity and target template complexity across the main conditions. Both accounts were refuted. It seems that when the identification of particular feature combinations is necessary, conjunction processing in audition becomes an effortful process.