Biomedical subjects

K Alho

Publications and source records attributed to K Alho.

98 records · Page 6Linked to original sources

PubMedDate not supplied

Mismatch negativity (MMN) for sequences of auditory and visual stimuli: evidence for a mechanism specific to the auditory modality.

ERPs to sequences of standard and deviant sinusoidal 100 msec tone pips, high-contrast sinusoidal gratings and to their simultaneously presented combinations were recorded. Mismatch negativity (MMN), an ERP component elicited by deviant stimuli, was estimated for the different stimulus sequences in order to find out whether it reflects modality-specific processes or non-specific attentive phenomena. In addition to the auditory modality, we studied whether the mismatch response could be evoked by a deviant visual stimulus in a visual sequence or by a deviant stimulus in either modality. The results show that only auditory stimuli produced the mismatch response, suggesting that MMN is not a manifestation of a general attentional mechanism but is probably specific to the auditory modality.

Acoustic Stimulation↗

PubMedDate not supplied

Event-related brain potential of human newborns to pitch change of an acoustic stimulus.

We report here event-related potentials (ERPs) of human newborns to occasional pitch changes in a repetitive sequence of tone pips. These pitch changes elicited a large slow negative ERP component which resembles the mismatch negativity (MMN) generated by the adult brain under similar conditions. This MMN-type of negativity in newborns suggests that already at this early ontogenetic stage the brain monitors the acoustic environment for a possible change in any of its repetitive aspects. Apart from its theoretical interest, this finding might provide a new way to test the development of the central nervous system and to diagnose cerebral dysfunction at a very early stage.

Acoustic Stimulation↗

PubMedDate not supplied

Neural plasticity in processing of sound location by the early blind: an event-related potential study.

Event-related potentials (ERPs) to a change in the locus of origin of a repetitive sound were studied in early blind human subjects. It was found that the N2b component of the ERP was posteriorly distributed on the scalp to that in the sighted control subjects. This suggests that the blind might use, to a larger extent than the sighted, parietal, or perhaps even occipital, brain areas in sound localization. The present results thus appear to demonstrate plastic changes in neural populations involved in processing of auditory space following early loss of vision.

Acoustic Stimulation↗

PubMedDate not supplied

Dose-related effect of alcohol on mismatch negativity and reaction time performance.

In a recent study, the mismatch negativity (MMN) component of auditory event-related potential, elicited by occasional frequency changes in a repetitive tone, was strongly attenuated by a low dosage of alcohol. We investigated the phenomenon in nine subjects with two different dosages of ethanol (0.35 and 0.55 g/kg), and with two magnitudes of frequency changes (5% and 10%), in a single-blind, placebo-controlled paradigm. Ethanol had no observable effect on the N1 and P2 deflections, nor on the reaction time to frequency changes measured in a separate session. However, the MMN was attenuated after administration of the larger dosage of alcohol, suggesting impaired preconscious processing of stimulus features outside the scope of attention. The results support the view according to which the automatic functions of human information processing are more sensitive than the controlled functions to the detrimental effects of alcohol. The fact that the MMN suppression was stronger when stimulus deviation was smaller indicates that at relatively low blood alcohol concentrations the detection of small deviations is especially hampered.

Acoustic Stimulation↗

PubMedDate not supplied

Effects of ethanol and auditory distraction on forced choice reaction time.

Effects of ethanol (0.55 g/kg) and auditory distraction on visual forced choice reaction time (RT) were investigated in 10 healthy social drinkers, using a single-blind, placebo-controlled, crossover design. Subjects were to respond by pressing a button either with their right-hand index or middle finger, depending on whether an odd or an even digit was presented on a PC screen. In control blocks, the digits were presented alone, whereas in distraction blocks they were shortly preceded by either a frequent "standard" tone of 600 Hz, or an infrequent tone that was either a 660 Hz "deviant" tone or a "novel" sound (e.g., telephone ringing). Alcohol reduced the hit rate by increasing the amount of errors, but had no effect on the RT, thus supporting the previous observations. In the placebo condition, the RT was prolonged by the deviant and novel sounds, and the hit rate was reduced by the deviant tones. During ethanol intoxication, however, the reduction in hit rate caused by the deviant tones was significantly smaller. This suggests that the attention-capturing effects of the deviant sounds were suppressed by ethanol, thus demonstrating a detrimental effect of ethanol on involuntary attention.

Acoustic Stimulation↗

PubMedDate not supplied

Aging effects on auditory processing: an event-related potential study.

Deviant tones randomly embedded in a sequence of standard tones elicit an event-related potential (ERP) called the mismatch negativity (MMN), which reflects automatic stimulus-change detection in the human auditory system. When the tones are attended, deviant tones elicit also an N2b component that partly overlaps the MMN. Sequences of standard and deviant (probability 0.15) tones were presented to 13 healthy younger and 13 older subjects. Deviant stimuli were, in separate blocks, either occasional shorter duration or higher frequency tones. The interstimulus interval (ISI) was, in separate blocks, either 0.5 s or 1.5 s, and in the frequency-change condition also 4.5 s. Aging affected neither frequency nor duration of MMN with the 0.5 s ISI. This finding indicates that automatic stimulus discrimination per se is not impaired with normal aging. However, with a 4.5-s ISI the MMN/N2b-complex attenuated significantly more in the older than younger subjects. This suggests that the stimulus trace decays faster or that involuntary attention switching is less sensitive with aging.

Acoustic Stimulation↗

PubMedDate not supplied

Involuntary attention and distractibility as evaluated with event-related brain potentials.

This article reviews recent event-related brain potential (ERP) studies of involuntary attention and distractibility in response to novelty and change in the acoustic environment. These studies show that the mismatch negativity, N(1) and P(3a) ERP components elicited by deviant or novel sounds in an unattended sequence of repetitive stimuli index different processes along the course to involuntary attention switch to distracting stimuli. These studies used new auditory-auditory and auditory-visual distraction paradigms, which enable one to assess objectively abnormal distractibility in several clinical patient groups, such as those suffering from closed-head injuries or chronic alcoholism.

Attention↗

PubMedDate not supplied

Mismatch negativity--the measure for central sound representation accuracy.

The mismatch negativity (MMN), elicited by any discriminable change in a repetitive sound even when this sound is not attended to, provides a pre-perceptual physiological measure of the accuracy of the central sound representation in the human brain. This accuracy, which can be measured separately for the different features of the sound, determines the individual's sound discrimination accuracy in normal and various pathological conditions.

Attention↗