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C Alain

Publications and source records attributed to C Alain.

At least 19 recordsLinked to original sources
PubMed2001

"What" and "where" in the human auditory system.

The extent to which sound identification and sound localization depend on specialized auditory pathways was examined by using functional magnetic resonance imaging and event-related brain potentials. Participants performed an S1-S2 match-to-sample task in which S1 differed from S2 in its pitch and/or location. In the pitch task, participants indicated whether S2 was lower, identical, or higher in pitch than S1. In the location task, participants were asked to localize S2 relative to S1 (i.e., leftward, same, or rightward). Relative to location, pitch processing generated greater activation in auditory cortex and the inferior frontal gyrus. Conversely, identifying the location of S2 relative to S1 generated greater activation in posterior temporal cortex, parietal cortex, and the superior frontal sulcus. Differential task-related effects on event-related brain potentials (ERPs) were seen in anterior and posterior brain regions beginning at 300 ms poststimulus and lasting for several hundred milliseconds. The converging evidence from two independent measurements of dissociable brain activity during identification and localization of identical stimuli provides strong support for specialized auditory streams in the human brain. These findings are analogous to the "what" and "where" segregation of visual information processing, and suggest that a similar functional organization exists for processing information from the auditory modality.

Acoustic Stimulation↗
PubMed2001

Binding occurs at early stages of processing in children and adults.

Conjoining features in a high-rate serial presentation was studied in children and adults using event-related potentials. Three blocks of trials were run in which targets were defined by colour, by orientation or by a conjunction of colour and orientation. Only adults had faster RTs when detecting targets defined by a single feature than by a combination of features. Compared with adults, children had longer RTs, longer N1 and P2 latencies, and larger P1 and P2 amplitudes. Amplitudes asymmetries were consistent with differing cortical regions being implicated in the processing of colour and form. There were, however, no ERP latency effects as a function of task, suggesting that the binding of features proceeds in parallel with the processing of single features.

Adult↗
PubMed2001

Conjoining three auditory features: an event-related brain potential study.

The mechanisms of auditory feature processing and conjunction were examined with event-related brain potential (ERP) recording in a task in which participants responded to target tones defined by the combination of location, frequency, and duration features amid distractor tones varying randomly along all feature dimensions. Attention effects were isolated as negative difference (Nd) waves by subtracting ERPs to tones with no target features from ERPs to tones with one, two, or three target features. Nd waves were seen to all tones sharing a single feature with the target, including tones sharing only target duration. Nd waves associated with the analysis of frequency and location features began at latencies of 60 msec, whereas Nd-Duration waves began at 120 msec. Nd waves to tones with single target features continued until 400+ msec, suggesting that once begun, the analysis of tone features continued exhaustively to conclusion. Nd-Frequency and Nd-Human Location waves had distinct scalp distributions, consistent with generation in different auditory cortical areas. Three stages of feature processing were identified: (1) Parallel feature processing (60-140 msec): Nd waves combined linearly, such that Nd-wave amplitudes following tones with two or three target features were equal to the sum of the Nd waves elicited by tones with only one target feature. (2) Conjunction-specific (CS) processing (140-220 msec): Nd amplitudes were enhanced following tones with any pair of attended features. (3) Target-specific (TS) processing (220-300 msec): Nd amplitudes were specifically enhanced to target tones with all three features. These results are consistent with a facilitatory interactive feature analysis (FIFA) model in which feature conjunction is associated with the amplified processing of individual stimulus features. Activation of N-methyl-D-aspartate (NMDA) receptors is proposed to underlie the FIFA process.

Adult↗
PubMed2001

Auditory feature conjunction in patients with schizophrenia.

The neural mechanisms supporting performance during single feature and feature conjunction tasks were investigated in patients with schizophrenia and age-matched controls using event-related brain potentials. In different blocks of trials, participants responded to auditory targets defined by one of two pitches, one of two locations, or both pitch and location. All participants were faster and more accurate in detecting targets defined by a single feature than for targets defined by a conjunction of features. Compared with the single feature conditions, conjunction targets were associated with enhanced negativity between 200 and 250ms (N2) post-stimulus and showed a delayed P3b latency. Compared with controls, patients with schizophrenia showed reduced N1 and N2 amplitude elicited by single and conjunctive targets. The results are consistent with defective perceptual mechanisms in schizophrenia. The fact that both performance and P3b amplitude were similar in patients and controls suggests that controlled processes compensate for processes normally carried out by early perceptual mechanisms.

Adult↗
PubMed2001

Attentional set modulates visual areas: an event-related potential study of attentional capture.

The present experiment offers event-related potential evidence suggesting that modulation of neural activity in the visual cortex underlies top-down attentional capture by irrelevant cues. Participants performed a covert visual search task where they identified the unique stimulus in a brief, four-location display. Targets defined uniquely by color or onset were run in separate blocks, encouraging observers to adopt different attentional sets in each block. In Experiment 1, a brief, white, abrupt-onset cue highlighted one of the locations 100 or 200 ms prior to the target display. In Experiment 2, the cue display consisted of three white and one red cues simultaneously presented at the four locations. In both experiments, participants were informed that there was no predictive relation between the location of the cue and that of the target. Reaction times were dependent on the location of the preceding cue (i.e. attention was captured), but only in those blocks where the cue shared the uniquely relevant target feature. Evoked potentials over the right hemisphere were modulated during the attention-capturing blocks just prior to the cue's appearance. Additionally, the N1 wave elicited by the cue was enhanced over occipital regions during the attention-capturing blocks. These findings support the notion that attentional capture with peripheral cues is not simply reflexive but is modulated by top-down processes.

Adolescent↗
PubMed2001

Location and frequency cues in auditory selective attention.

The roles of frequency and location cues in auditory selective attention were investigated in a series of experiments in which target tones were distinguished from distractors by frequency, location, or the conjunction of frequency and location features. When frequency separations in high-rate tone sequences were greater than 1 octave, participants were fastest at identifying targets defined by frequency and were sometimes faster at identifying conjunction than location targets. Frequency salience diminished as filtering demands were reduced: At long interstimulus intervals (> 2.0 s), performance was superior in location conditions. The results suggest that frequency may play a role in auditory selective attention tasks analogous to the role of spatial position in visual attention.

Adolescent↗
PubMed2001

Bottom-up and top-down influences on auditory scene analysis: evidence from event-related brain potentials.

The physiological processes underlying the segregation of concurrent sounds were investigated through the use of event-related brain potentials. The stimuli were complex sounds containing multiple harmonics, one of which could be mistuned so that it was no longer an integer multiple of the fundamental. Perception of concurrent auditory objects increased with degree of mistuning and was accompanied by negative and positive waves that peaked at 180 and 400 ms poststimulus, respectively. The negative wave, referred to as object-related negativity, was present during passive listening, but the positive wave was not. These findings indicate bottom-up and top-down influences during auditory scene analysis. Brain electrical source analyses showed that distinguishing simultaneous auditory objects involved a widely distributed neural network that included auditory cortices, the medial temporal lobe, and posterior association cortices.

Adult↗
PubMed2001

Age-related changes in detecting a mistuned harmonic.

The effects of age on discriminating simultaneous sounds were investigated by comparing the hearing threshold in detecting a mistuned harmonic in young, middle-aged, and older adults. The stimuli were complex sounds containing multiple harmonics, one of which could be "mistuned" so that it was no longer an integer multiple of the fundamental. Older adults had higher thresholds than middle-aged or young adults. The effect of age was greater for short than for long duration sounds and remained even after controlling for hearing sensitivity. The results are consistent with an age-related decline in parsing simultaneous auditory events, which may contribute to the speech perception difficulties in the elderly.

Adult↗
PubMed2000

Effects of task context and fluctuations of attention on neural activity supporting performance of the stroop task.

The influence of task context and transient fluctuations in attentional control on neural processes supporting performance of the Stroop task was investigated using event-related brain potentials. Task context was manipulated by varying the proportion of congruent and incongruent trials across different blocks of trials, and fluctuations of attentional control were considered by examining differences between trials eliciting faster and slower responses. The amplitudes of the N450, thought to reflect the suppression of a conceptual level processing system, and a temporo-parietal slow wave, thought to index the processing of color information, were greater when trials were mostly congruent in comparison to when trials were mostly incongruent. These findings indicate that the neural systems supporting inhibition and color processing are modulated by task demands. For the N450 the effect of task context interacted with the efficiency of attentional control being present for those trials eliciting faster responses and not for those trials eliciting slower responses. This finding is consistent with those from a growing number of studies indicating that the neural systems supporting attentional control are transient in nature, tending to fluctuate in efficiency over time.

Adult↗
PubMed2000

Effects of visual attentional load on auditory processing.

Auditory evoked potentials were recorded while participants attended to visually presented digits. The difficulty of the visual task was manipulated by requiring participants to process only the current digit (0-back) or both the current and the preceding digit (1-back). Tones deviating in frequency from standard tones elicited a frontal mismatch negativity peaking around 200 ms which did not vary with visual task. However, decreasing the visual task load enhanced a right-temporal positive wave peaking around 200 ms when tones were presented slowly, and a frontocentral negative wave peaking around 450 ms when tones were presented more rapidly. The degree to which task-irrelevant sounds are processed therefore depends on the degree to which a visual task engages attentional resources.

Adult↗
PubMed2000

Selectively attending to auditory objects.

The ability to maintain a conversation with one person while at a noisy cocktail party has often been used to illustrate a general characteristic of auditory selective attention, namely that perceivers' attention is usually directed to a particular set of sounds and not to others. Part of the cocktail party problem involves parsing co-occurring speech sounds and simultaneously integrating these various speech tokens into meaningful units ("auditory scene analysis"). Here, we review auditory perception and selective attention studies in an attempt to determine the role of perceptual organization in selective attention. Results from several behavioral and electrophysiological studies indicate that the ability to focus attention selectively on a particular sound source depends on a preliminary analysis that partitions the auditory input into distinct perceptual objects. Most findings can be accounted for by an object-based hypothesis in which auditory attention is allocated to perceptual objects derived from the auditory scene according to perceptual grouping principles.

Attention↗
PubMed2000

Evidence for the transient nature of a neural system supporting goal-directed action.

Disruption of a neural system supporting goal-directed action gives rise to lapses of intention in healthy individuals and disorganized behavior in patients with prefrontal lesions. Evidence from behavioral studies indicates that the occurrence of lapses in selective attention, working memory and prospective memory tasks is transient in nature. In the current study, we used event-related brain potentials to demonstrate that lapses are associated with a slow wave over the frontal region that begins well before stimulus onset and lasts for several hundred milliseconds. The magnitude of this slow wave was modulated by task demands, indicating that attentional processes can be flexibly allocated in the service of goal-directed action. Together the findings of these experiments indicate that lapses result from a transient inability to bring to bear the goals of the individual upon the action selection system.

Adult↗
PubMed2000

Age-related decline in inhibitory control contributes to the increased Stroop effect observed in older adults.

Past research has demonstrated an age-related increase in the Stroop effect. Some theorists have suggested that this increase results from a decline in the ability to inhibit word information on incongruent trials, whereas others have suggested that the decline reflects general slowing. These two hypotheses were evaluated using event-related brain potentials (ERPs) measured while younger and older adults performed the Stroop task. As expected, the Stroop effect was greater for older than younger adults. The ERP data revealed a selective age-related attenuation of two modulations reflecting the inhibition of word information on incongruent trials. Latency of the P3 wave did not increase to a greater extend for older than younger adults from the congruent to incongruent trials as expected based on the general slowing hypothesis. Taken together, these findings support the inhibitory deficit hypothesis by demonstrating an age-related decline in a conceptual level inhibitory process that supports the suppression of word information in the Stroop task.

Adult↗
PubMed1999

Global and local processing of musical sequences: an event-related brain potential study.

Musical processing can be decomposed into the appreciation of global/holistic and local elements. Here, we investigated the pattern of neural activity associated with the processing of contour-violated (CV) and contour-preserved (CP) melodies. The CV and CP musical sequences were obtained by altering the pitch value of one note within the musical phrase, while keeping both the scale and the key constant. In the unadulterated melody, there was a sustained negativity that was larger over the right than left fronto-central regions. Participants were equally accurate in detecting CV and CP trials, but were slower in detecting CP than CV trials. Globally altered melodies (i.e. CV) generated an early, negative waveform (N2) and a P3b deflection, whereas the CP target only generated a P3b wave. This suggests that global precedence may occur at an early perceptual stage and argues in favor of fractionating musical processing into global and local components.

Adult↗
PubMed1999

Event-related brain activity associated with auditory pattern processing.

One of the basic properties of the auditory system is the ability to analyze complex temporal patterns. Here, we investigated the neural activity associated with auditory pattern processing using event-related brain potentials. Participants were presented with a continuously repeating sequence of four tones with rare changes in either the frequency or timing of one of the tones. Both frequency- and time-deviant sounds generated mismatch negativity (MMN) waves that peaked at midline central electrode sites and inverted in polarity at inferior temporal and occipital sites, consistent with generators in the supratemporal plane. The MMN scalp topography was similar for the frequency- and time-deviant stimuli, suggesting that both spectral and temporal relations among elements of an auditory pattern are encoded in a unified memory trace.

Acoustic Stimulation↗
PubMed1999

Event-related neural activity associated with the Stroop task.

The time course of neural activity supporting performance during the Stroop task was investigated using event-related brain potentials (ERPs). Four spatially and temporally distinct modulations were observed differentiating the ERPs elicited by incongruent trials from the ERPs elicited by congruent, neutral, or word identification trials. Two of these modulations reflected increased negativity over the fronto-central region and positivity over the fronto-polar region for incongruent trials and may reflect conflict detection and resolution processes. The other modulations, distributed over the left parietal and temporo-parietal regions, may reflect the activity of a meaning-based conceptual level system active during congruent, neutral, and word identification trials; and the activity of a perceptual level system supporting task performance when only color information can guide an efficient response on incongruent trials.

Adult↗
PubMed1999

Binding visual features during high-rate serial presentation.

The neural mechanism supporting performance during single and feature conjunction detection was investigated using event-related brain potentials. In different blocks of trials, participants responded to visual targets defined by one of two colors, one of two orientations, or both color and orientation. Participants were faster and more accurate in detecting targets defined by a single feature than for targets defined by a conjunction of features. Compared with the single feature conditions, conjunction targets were associated with enhanced negativity between 230 and 270 ms post-stimulus and showed a delayed P3 latency. The relative timing of feature specific attention effects isolated in difference potential shows that feature conjunction occurs concurrently with the analysis of single features.

Adult↗