Allan J. Nash

P300 and allocation of attention in dual-tasks

P300 in dual-tasks has been reported to be distributed reciprocally across the tasks, i.e. larger P300 associated with one task implies smaller P300 associated with the other (Wickens et al., 1983; Sirevääg et al., 1989). In these studies, however, the dual-tasks stimuli were either presented simultaneously, precluding a direct, within-trial assessment of relative magnitudes of P300, or they were separated by intervals of 1 s or more, thereby minimizing overlap of the ERP epochs, but at the cost of reduced competition for shared processing resources. The present experiment used an inter-stimulus interval of 400 ms between the auditory (tones) and visual (colored LEDs) stimuli that defined the dual-task and found that, when deviant tones elicited a prominent auditory P300, they were followed by a greatly reduced P300 for the deviant LED. The findings were interpreted from viewpoints that considered the effects of neural inhibition versus neural recovery cycles on the amplitude of P300.

Effects of preparatory set and task demands on auditory event-related potentials

Different instructional sets for moderate vs. high response speeds were given in a visual letter-matching task. On 50 percent of the trials an auditory probe requiring a simple RT response was presented in one of four temporal locations within the ongoing visual task. Probe locations were selected to maximize differences in the processing demands of the dual, auditory-visual task (see Posner and Boies, 1971). The N100 of the event-related potential associated with the auditory probe was larger under the high response speed set than under the moderate set, regardless of probe location. P300 amplitude was also greater under the high speed set relative to the moderate set but only when the task demands were high. The results were interpreted in terms of the interaction between arousal and task demands and a neural inhibition model of the P300 was discussed.

Emotionally negative pictures increase attention to a subsequent auditory stimulus.

Emotionally negative stimuli serve as a mechanism of biological preparedness to enhance attention. We hypothesized that emotionally negative stimuli would also serve as motivational priming to increase attention resources for subsequent stimuli. To that end, we tested 11 participants in a dual sensory modality task, wherein emotionally negative pictures were contrasted with emotionally neutral pictures and each picture was followed 600 ms later by a tone in an auditory oddball paradigm. Each trial began with a picture displayed for 200 ms; half of the trials began with an emotionally negative picture and half of the trials began with an emotionally neutral picture; 600 ms following picture presentation, the participants heard either an oddball tone or a standard tone. At the end of each trial (picture followed by tone), the participants categorized, with a button press, the picture and tone combination. As expected, and consistent with previous studies, we found an enhanced visual late positive potential (latency range=300-700 ms) to the negative picture stimuli. We further found that compared to neutral pictures, negative pictures resulted in early attention and orienting effects to subsequent tones (measured through an enhanced N1 and N2) and sustained attention effects only to the subsequent oddball tones (measured through late processing negativity, latency range=400-700 ms). Number pad responses to both the picture and tone category showed the shortest response latencies and greatest percentage of correct picture-tone categorization on the negative picture followed by oddball tone trials. Consistent with previous work on natural selective attention, our results support the idea that emotional stimuli can alter attention resource allocation. This finding has broad implications for human attention and performance as it specifically shows the conditions in which an emotionally negative stimulus can result in extended stimulus evaluation.

The late positive components of the human EEG in a signal detection task

Abstract In 1971, Hillyard, Squires, Bauer and Lindsay using human subjects in a signal detection task, obtained a prominent late positive component (LPC) of the EEG only in the Hit category of responses. They concluded that the LPC reflects the subjects degree of certainty that a signal has occurred. In contrast the present study observed the LPC in the Hit, Miss, and Correct Rejection categories of responses, supporting the hypothesis that the LPC is a correlate of uncertainty reduction and does not directly depend on the physical presence of the signal.

HIV-positive females show blunted neurophysiological responses in an emotion–attention dual task paradigm

OBJECTIVE Although HIV is associated with decreased emotional and cognitive functioning, the mechanisms through which affective changes can alter cognitive processes in HIV-infected individuals are unknown. We aimed to clarify this question through testing the extent to which emotionally negative stimuli prime attention to a subsequent infrequently occurring auditory tone in HIV+ compared to HIV- females. METHODS Attention to emotional compared to non-emotional pictures was measured via the LPP ERP. Subsequent attention was indexed through the N1 and late processing negativity ERP. We also assessed mood and cognitive functioning in both groups. RESULTS In HIV- females, emotionally negative pictures, compared to neutral pictures, resulted in an enhanced LPP to the pictures and an enhanced N1 to subsequent tones. The HIV+ group did not show a difference in the LPP measure between picture categories, and accordingly, did not show a priming effect to the subsequent infrequent tones. CONCLUSIONS The ERP findings, combined with neuropsychological deficits, suggest that HIV+ females show impairments in attention to emotionally-laden stimuli and that this impairment might be related to a loss of affective priming. SIGNIFICANCE This study is the first to provide physiological evidence that the LPP, a measure of attention to emotionally-charged visual stimuli, is reduced in HIV-infected individuals. These results set the stage for future work aimed at localizing brain activation to emotional stimuli in HIV+ individuals.

The late positive component of the auditory evoked potential in a shared reading and counting task

Abstract Eight subjects were presented with a series of low and high tones. When they were instructed to ignore the tones and perform a reading task, the late positive component (LPC) of the evoked EEG was absent. Both tones, however, produced LPCs when S counted the higher tone, with the counted tone showing greater LPC amplitude. Under a shared reading and counting task, LPC amplitudes were reduced and comparable to those observed in the read-only condition. These results were interpreted as most consistent with a selective attention hypothesis of the LPC.

The effects of magnitude and direction of stimulus change on auditory event-related potentials elicited by deviant signal stimuli

The present study sought to identify components of the auditory event-related potential (ERP) elicited by stimuli that serve as signals for overt discriminative responses. Sokolovs view of a selective neural filter for deviant stimuli predicts that responses to deviant signal stimuli will be graded in proportion to the amount of change from the standard and independent of the direction of that change. The demonstration of a bi-directional and graded ERP response requires at least two levels of stimulus change in each direction. The present study incorporated two deviants that were lower in pitch (lowest, low) and two that were higher in pitch (high, highest) in order to evaluate the degree (linear, quadratic, etc.) of the function relating ERP response to tonal deviance. Stimulus changes on both the direction and magnitude dimensions were also varied on a trial-by-trial, rather than on a block-by-block, basis which eliminated potential confounds with block or session differences, and discriminative responses were required to both standard and deviant tones, thereby investing both categories of stimuli with signal value. The amplitude of the P3 component associated with deviant stimuli showed close correspondence to the (quadratic) function predicted from the selective filter model. A late negative slow wave (NSW) at Fz and a positive slow wave (PSW) at Pz differentiated deviant tones from the standard but did not distinguish between the deviants themselves. A fronto-central NSW observed at Fz and Cz for initial standard tones was greater than the predominantly frontal NSW elicited by the deviant tones. The topographical differences in NSW elicited by the initial standard tone and by all deviant tones suggest that different processes are reflected in the NSW response to these stimuli.

Effects of information feedback and reference tones on signal detection

In an auditory signal detection study feedback and no-feedback conditions were compared and the effect of introducing anchor or reference tones during the intertrial interval was investigated. Feedback increased the proportion of correct detections as did the presence of a strong anchor. The latter condition was also associated with a reduction of false alarms.

Response probabilities for individual stimuli in learning tasks

Four squirrel monkeys were tested on a series of five learning problems. The first three problems involved the discrimination of two stimuli while each of the last two problems consisted of 10 stimuli divided into two response classes. Analysis of the proportion of correct responses to individual stimuli within a problem set revealed strong position-habit errors and suggested that S does not learn the correct response to all stimuli of the same problem set with equal facility. This differential level of responding was more pronounced for the 10-stimulus problems than for the 2-stimulus problems.

A sequential test of performance (STOP) for all-or-none learning data

A procedure is developed using the binomial test for the sequential criterion testing of all-or-none learning data. The sequential test is accompanied by a format for gathering the data which generates a graphic profile of S’s performance over trials. Comparison of an index of problem difficulty provided by the Sequential Test of Performance (STOP) with a more commonly used index, the number of correct responses in a fixed block of trials, produced a high linear relationship between the two measures with the STOP method showing a savings in trials run of over 40%.