Biomedical subjects

Alexandra Muller-Gass

Publications and source records attributed to Alexandra Muller-Gass.

4 recordsLinked to original sources

PubMed2007

Perceptual and cognitive task difficulty has differential effects on auditory distraction.

When a task-irrelevant feature of an auditory stimulus varies at rare and unpredictable times, the processing of this change interferes with the processing of task-relevant stimulus information. The present study investigated whether this distraction effect is modulated by the difficulty of the auditory task. Event-related potentials (ERPs) and behavioral responses were recorded while subjects classified stimuli based on their temporal dimension. In one condition, the task was made more difficult by decreasing the perceptual discriminability (temporal distinctiveness) of the stimuli. In a second condition, the difficult task involved an increase in memory load: subjects were asked to assess the duration of the current compared to that of the previous stimulus. The occurrence of an infrequent task-irrelevant change in the pitch of the stimulus caused distraction in all task conditions. Following this change, performance deteriorated, and a distinct P3a component was visible in the ERP. Importantly, the extent of this distraction effect was significantly enhanced during the high memory load task, but not during the difficult perceptual task. It may be that the attentional resources afforded to the stimuli, rather than task difficulty, affected the extent of the distraction response. When the processing requirements of a task demand more highly focused attention for stimulus processing, the processing of the distracting information embedded within this stimulus may inadvertently also benefit from this attention.

Acoustic Stimulation↗

PubMed2006

The effect of visual task difficulty and attentional direction on the detection of acoustic change as indexed by the Mismatch Negativity.

Näätänen's model of auditory processing purports that attention does not affect the MMN. The present study investigates this claim through two different manipulations. First, the effect of visual task difficulty on the passively elicited MMN is assessed. Second, the MMNs elicited by stimuli under attended and ignored conditions are compared. In Experiment 1, subjects were presented with mixed sequences of equiprobable auditory and visual stimuli. The auditory stimuli consisted of standard (80 dB SPL 1000 Hz), frequency deviant (1050 Hz), and intensity deviant (70 dB SPL) tone pips. In a first instance, subjects were instructed to ignore the auditory stimulation and engage in an easy and difficult visual discrimination task (focused condition). Subsequently, they were asked to attend to both modalities and detect visual and auditory deviant stimuli (divided condition). The results indicate that the passively elicited MMN to frequency and intensity deviants did not significantly vary with visual task difficulty, in spite of the fact that the easy and difficult tasks showed a wide variation in performance. The manipulation of the attentional direction (focused vs. divided conditions) did result in a significant effect on the MMN elicited by the intensity, but not frequency, deviant. The intensity MMN was larger at frontal sites when subjects' attention was directed to both modalities as compared to only the visual modality. The attentional effect on the MMN to the intensity deviants only may be due to the specific deviant feature or the poorer perceptual discriminability of this deviant from the standard. Experiment 2 was designed to address this issue. The methods of Experiment 2 were identical to those of Experiment 1 with the exception that the intensity deviant (60 dB SPL) was made to be more perceptible than the frequency deviant (1016 Hz) when compared to the standard stimulus (80 dB SPL 1000 Hz). The results of Experiment 2 also demonstrated that the passively elicited MMN was not affected by large variations in visual task difficulty; this provides convincing evidence that the MMN is independent of visual task demands. Similarly to Experiment 1, the direction of attention again had a significant effect on the MMN. In Experiment 2, however, the frequency MMN (and not the intensity MMN) was larger at frontal sites during divided attention compared to focused visual attention. The most parsimonious explanation of these results is that attention enhances the discriminability of the deviant from the standard background stimulation. As such, small acoustic changes would benefit from attention whereas the discriminability of larger changes may not be significantly enhanced.

Acoustic Stimulation↗

PubMed2005

"...and were instructed to read a self-selected book while ignoring the auditory stimuli": the effects of task demands on the mismatch negativity.

OBJECTIVE: The Mismatch Negativity (MMN) is commonly recorded while the subject is reading, and instructed to ignore the auditory stimuli. It is generally assumed that the demands of the diversion task will have no effect on the MMN. Several studies, however, have reported that a diversion task presumably requiring strong attentional focus is associated with a smaller MMN than that elicited during a less demanding task. This study examines the effect of variations in the classical reading paradigm on the MMN. METHODS: In Experiment 1, event-related potentials (ERP) were recorded while subjects were presented with standard (80 dB SPL 1000 Hz) and frequency deviant (1050 Hz) stimuli. Subjects were instructed to ignore the tone pips and, in separate conditions, engage in different tasks. They were asked to read a text or to sit passively. Subjects were informed that they would subsequently be queried or not about the content of the reading. In Experiment 2, the auditory sequence included the same standard (80 dB SPL 1000 Hz) but the deviant was changed to an intensity decrement (70 dB SPL). A different sample of subjects was again asked to ignore the auditory stimuli and engage in different reading tasks that would or not be followed by query. RESULTS: In all task conditions, MMN was elicited by the frequency and intensity change. The intensity MMN did not significantly vary with task. A significant effect of task was, however, found for the frequency MMN. Its amplitude was largest when subjects were later queried about their reading. CONCLUSIONS: This finding is counter-intuitive in light of previous research on the attentional modulation of the MMN. The pattern of frequency MMN results may relate to the differences in cortical excitability across tasks. SIGNIFICANCE: The present results indicate that the nature of the diversion task may affect the MMN. The choice of diversion task during MMN recording should thus be carefully considered.

Acoustic Stimulation↗

PubMed2002

Event-related potential measures of the inhibition of information processing: I. Selective attention in the waking state.

This article reviews the effects of selective attention on event-related potentials (ERPs). Attention has little, if any, effect on short-latency exogenous ERPs. The longer-latency ERPs can be markedly affected by manipulation of the subject's level of attention. For example, a late positive wave, P300, appears to occur only if subjects actively detect an infrequently occurring target stimulus. However, a number of other late positive waves may also occur independently of the direction of attention, particularly if elicited by highly biologically or psychologically relevant stimuli. Attention may also interact with an earlier, apparently exogenous, negative waveform, N1. This could be due to the overlapping and summating effect of an attentional-related waveform, the processing negativity. The presentation of a physically deviant stimulus occurring among a train of homogeneous standard stimuli will elicit another negative wave, the mismatch negativity (MMN). The MMN has traditionally been thought to occur independently of attention. More recent studies have, however, shown that attention can modulate the MMN. This may, however, be explained by the summating effects of other overlapping components. Interpreting the scalp-recorded ERP can therefore require judicious care. Design of experiments must take into account the fact that the magnitude of attentional effects will depend on a number of different influences, some of which are very subtle and complex. A problem with any study in the waking and alert human is that the subject may not be able to completely ignore stimuli, in spite of instructions to do so. For this reason, the study of unconscious states, such as sleep, may prove to be especially fruitful in understanding the effects of attention in the waking state.

Animals↗