Biomedical subjects

L Y Deouell

Publications and source records attributed to L Y Deouell.

7 recordsLinked to original sources

PubMed2001

Is pre-attentive processing compromised by prolonged wakefulness? Effects of total sleep deprivation on the mismatch negativity.

We investigated the potential influence of sustained wakefulness on pre-attentive capacities by recording the mismatch negativity (MMN), an electrophysiological manifestation associated with nonintentional detection of auditory oddball stimuli. The MMN was elicited by pitch deviants presented to both ears via earphones, at the beginning of a total sleep deprivation session (baseline), after 24 hr, and after 36 hr of continuous controlled wakefulness. A conspicuous MMN response was elicited at all three sessions. With time, however, a small yet significant gradual reduction in the MMN amplitude was evident. Whereas previous research suggested that controlled attention-demanding tasks are hampered by sleep deprivation, the balance of the present results suggests that passive (total) sleep deprivation may also bring about some degradation in the pre-attentive detection of environmental irregularities and as a consequence may disrupt the reflexive shift of attention induced by such events.

Acoustic Stimulation↗

PubMed2000

What is extinguished in auditory extinction?

Extinction is a frequent sequel of brain damage, whereupon patients disregard (extinguish) a contralesional stimulus, and report only the more ipsilesional stimulus, of a pair of stimuli presented simultaneously. We investigated the possibility of a dissociation between the detection and the identification of extinguished phonemes. Fourteen right hemisphere damaged patients with severe auditory extinction were examined using a paradigm that separated the localization of stimuli and the identification of their phonetic content. Patients reported the identity of left-sided phonemes, while extinguishing them at the same time, in the traditional sense of the term. This dissociation suggests that auditory extinction is more about acknowledging the existence of a stimulus in the contralesional hemispace than about the actual processing of the stimulus.

Acoustic Stimulation↗

PubMed2000

Electrophysiological evidence for an early(pre-attentive) information processing deficit in patients with right hemisphere damage and unilateral neglect.

Patients with right hemisphere damage and contralesional neglect are often unaware of visual, auditory or tactile stimuli occurring on their left side. In an effort to understand the contribution of pre-attentive processes to this phenomenon, we examined the processing of the pitch, duration and spatial location of auditory stimuli using an electrophysiological probe, the mismatch negativity (MMN). This event-related brain potential indexes the integrity of cerebral processes that respond automatically to deviations from regularity in the acoustic environment. We compared the MMN elicited by right- and left-sided deviant stimuli in 10 patients with left unilateral neglect and 10 age-matched healthy volunteers, exploring an anticipated dissociation between the processing of spatial localization of sounds and the processing of the other auditory dimensions. Across dimensions, the MMN elicited by deviance occurring to the left of the patients was reduced relative to that elicited by deviance occurring to the right. This effect was robust for spatial location, and less so for pitch, whereas the processing of stimulus duration was not significantly affected by the side of stimulation. In healthy subjects, deviance in either side elicited similar MMN. We suggest that an early deficit in detecting changes in the environment hampers the involuntary triggering of attention in those patients and discuss the specific role of encoding spatial location in the establishment of conscious awareness.

Adult↗

PubMed1999

Selective visual streaming in face recognition: evidence from developmental prosopagnosia.

Computational considerations suggest that efficient face identification requires the categorization and exclusive streaming of previously encoded face visual primitives into a dedicated face recognition system. Unique evidence supporting this claim is provided by a rare case of developmental pure prosopagnosia with otherwise normal visual and cognitive functions. Despite his normal visual memory and ability to describe faces, he is extremely impaired in face recognition. An early event related brain potential (N170) that is normally elicited exclusively by human faces, showed no specificity in this person. MRI revealed a smaller then normal right temporal lobe. These data emphasize the indispensability of the early streaming process for face recognition.

Adult↗

PubMed1998

Mismatch negativity in dichotic listening: evidence for interhemispheric differences and multiple generators.

The characteristics of mismatch negativity (MMN) elicited by dichotic stimulation were examined using frequency-deviant stimuli presented to the right, to the left, or to both sides. The experiment was run twice, once using earphones and once using loudspeakers in free field. With both modes of stimulation, deviants presented in the left, right, or both ears, or tones that were switched between ears, elicited comparable MMNs, with a peak latency of about 180 ms. With earphones, the amplitude of the MMN was bigger at the frontal-lateral right hemisphere sites than at the homologous left-hemisphere sites for all deviance conditions. Scalp current density analysis revealed that deviance in the right side elicited bilaterally equivalent frontal current sinks and a trend towards stronger contralateral current sources at the mastoid sites. In contrast, left side deviance elicited frontal sinks and temporal current sources stronger over the right hemiscalp. These results are compatible with the multiple-generator model of MMN. The attention-related role of the MMN is discussed, suggesting comparable attention mechanisms for vision and audition.

Adult↗

PubMed1998

Variable cerebral responses to equally distinct deviance in four auditory dimensions: a mismatch negativity study.

In this study we compared the amplitude, latency, and spatial distribution of the mismatch negativity (MMN), elicited by tones deviating in either frequency, intensity, stimulus-onset asynchrony (SOA) or location, and assessed inter- and intra-subject variability. Cross-dimensional comparisons were facilitated by adjusting the magnitude of deviance individually, so that the detection rates were similar, both across dimensions (within subject) and across subjects (within dimension). Despite similar detection rates, the MMN elicited by frequency deviance was larger, and the MMN elicited by SOA deviance was earlier than the other types of MMN. The reliability of frequency-related MMN was better than that of the other types of MMN. The results highlight the problems of comparing MMN across dimensions, especially in clinical populations.

Adult↗

PubMedDate not supplied

Unilateral neglect after right-hemisphere damage: contributions from event-related potentials.

Unilateral neglect is a frequent sequel of right-hemisphere damage. Patients suffering from neglect may fail to detect, orient to, acknowledge or respond to stimuli on their contralesional side, even in the absence of primary sensory or motor loss. Despite the major clinical significance of the phenomenon and its potential implications for our understanding of human cognition, the underlying cognitive deficits are not well understood. We review the relatively few event-related potential studies that attempted to assess the different parts of the cognitive system in neglect patients. We suggest that theories of neglect, based primarily on performance data, may be refined by incorporating these results, and that this line of research may provide information that is not available using traditional performance measures.

Attention↗