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K Alho

Publications and source records attributed to K Alho.

At least 91 records · Page 5Linked to original sources
PubMed1992

Selective attention in auditory processing as reflected by event-related brain potentials.

Measures of event-related brain potentials (ERPs) have revealed two kinds of selective-attention mechanisms that operate on attended and unattended auditory stimuli. The processing negativity of the ERP reveals a mechanism of intramodal selective attention in the auditory cortex controlled by the frontal cortex. This mechanism selects attended auditory stimuli for further processing when they differ from unattended stimuli in location or tonal frequency. Studies of intermodal selective attention have compared auditory ERPs during auditory and visual attention. At least in part different brain mechanisms may be involved in the selection of auditory stimuli among other auditory stimuli (intramodal selective attention) and in the selection of auditory stimuli among visual stimuli (intermodal selective attention). This is suggested by the results showing that the earlier component of the processing negativity, which is generated in the auditory cortex during intramodal selective attention, differs in scalp distribution from the early attention-related negativity elicited during intermodal selective attention. With respect to the unattended auditory stimuli, ERP studies of selective attention suggest that physical features of these stimuli are extensively processed. This is shown by the mismatch negativity component of the ERP, which is usually elicited by infrequent physical deviations in an auditory stimulus sequence both when this sequence is attended and when it is ignored. This would be impossible if the physical stimulus features were not extensively processed, even in the absence of attention.

Arousal↗
PubMed1991

Right hemisphere dominance of different mismatch negativities.

Auditory stimulus blocks were presented to 10 reading subjects. Each block consisted of 2 types of stimulus, standard (P = 90%) and deviant (P = 10%), delivered in a random order with short constant inter-stimulus intervals. The standard stimuli were 600 Hz. 80 dB SPL 50 msec sine wave bursts. In different blocks, the deviant stimuli differed from the standards either in frequency (650 Hz), intensity (70 dB) or duration (20 msec). Left- and right-ear stimulations were used in separate blocks. Event-related brain potentials (ERPs) were recorded with 16 electrodes over both hemispheres. All the different types of deviant stimuli elicited an ERP component called the mismatch negativity (MMN). The MMN was larger over the right hemisphere irrespective of the ear stimulated whereas the N1 component, elicited by both standards and deviants, was larger over the hemisphere contralateral to the ear stimulated. The results provide further evidence for the view that the MMN reflects a neural mismatch process with a memory trace which automatically codes the physical features of the repetitive stimuli.

Acoustic Stimulation↗
PubMed1991

Brain potential signs of feature processing during auditory selective attention.

We recorded event-related brain potentials (ERPs) to random dichotic tone sequences as subjects attended to tone bursts of a designated pitch (250, 1000 or 4000 Hz) and ear of delivery. The effects of attention were isolated as negative difference (Nd) waves by subtracting ERPs to ignored tones from ERPs to the same tones when either one or both features were attended. Early sensory components of the ERP changed tonotopically in scalp distribution, while the distributions of Nd waves were feature-specific (pitch processing differed from location processing) but not tonotopic. At longer latencies, Nd waves specific to feature-conjunction operations were isolated. These began 40-50 ms after Nds to isolated cues and continued for hundreds of ms.

Acoustic Stimulation↗
PubMed1990

The effect of small variation of the frequent auditory stimulus on the event-related brain potential to the infrequent stimulus.

We investigated whether the mismatch process between a rare stimulus and the trace of the frequent stimulus, which generates the mismatch-negativity component of the event-related potential, can tolerate a small variation in the intensity of the frequent stimulus. Series of short tone pips were presented to 10 subjects while they were reading a book and ignoring the auditory stimuli. The intensity (mean 80dB) of the frequent stimulus (600 Hz) varied within a range that was different in different blocks. The probability of the infrequent stimuli which were, in different blocks, either intensity deviants (600 Hz/70dB) or frequency deviants (650 Hz/80dB) was 10%. Both deviant stimuli elicited mismatch negativity even when the intensity of the frequent stimulus varied, although the amplitude of this component decreased with the increasing variability of the frequent stimulus. These results show that the generator process of mismatch negativity tolerates some variation in the repetitive stimulus, thus indicating that this process is also activated in ecologically more valid conditions. This is crucial to the interpretation of the generator process of mismatch negativity as a biologically vital warning mechanism.

Adult↗
PubMed1990

Event-related brain potentials in selective listening to frequent and rare stimuli.

Our previous event-related brain potential (ERP) results suggest that during selective listening, relevant stimuli are selected for further processing by comparing each stimulus to an "attentional trace," a neuronal representation of the physical features of the relevant stimuli that distinguish them from the irrelevant stimuli. This comparison process is reflected by the early component of the processing negativity (PN), which is largest and longest to the relevant stimuli (perfectly matching with the trace). In the present study, the subjects selectively listened to designated tone stimuli which randomly appeared among irrelevant tones of a different pitch. The probability of relevant stimuli in a block was varied. The processing negativity elicited by relevant stimuli was smaller the less frequent they were. The results support the attentional-trace theory of selective attention, which proposes that, in addition to active maintenance, the trace also depends on the rate of sensory reinforcement provided by the relevant stimuli.

Acoustic Stimulation↗
PubMed1989

Do event-related potentials reveal the mechanism of the auditory sensory memory in the human brain?

Event-related brain potentials (ERP) to task-irrelevant tone pips presented at short intervals were recorded from the scalp of normal human subjects. Infrequent decrements in stimulus intensity elicited the mismatch negativity (MMN) which was larger in amplitude and shorter in latency the softer the deviant stimulus was. The results obtained imply memory representations which develop automatically and accurately represent the physical features of the repetitive stimulus. These memory traces appear to be those of the acoustic sensory memory, the 'echoic' memory. When an input does not match with such a trace the MMN is generated.

Acoustic Stimulation↗
PubMed1989

Event-related brain potentials reflecting processing of relevant and irrelevant stimuli during selective listening.

Event-related brain potentials were recorded from the human scalp during selective listening to tone pips differing in location and/or pitch from irrelevant tones. The subjects' task was to discriminate infrequent deviant tones of lower intensity appearing among designated (relevant) tones. A large processing negativity was observed in the event-related potentials to relevant tones differing from the irrelevant tones in location even when both tones randomly varied in pitch. Similarly, a large processing negativity was elicited by the relevant tones differing from the irrelevant tones in pitch even when the location of both tones varied randomly. The results support the theory that the processing negativity to relevant stimuli reflects a match of these stimuli with an "attentional trace," an actively maintained neuronal representation of the physical feature(s) of relevant stimuli that distinguish these stimuli from the irrelevant stimuli. Furthermore, the infrequent lower-intensity tones appearing among irrelevant tones elicited a mismatch negativity similar to the mismatch negativity elicited by target tones, equivalent lower-intensity tones appearing among relevant tones. This indicates that these infrequent stimulus changes were automatically discriminated by the generator mechanism associated with mismatch negativity.

Adult↗
PubMed1988

Frequency and location specificity of the human vertex N1 wave.

Test tones of 1000 Hz subjectively located in the middle of the head were randomly presented with equiprobable intervening tones. The latter stimulus was constant within a stimulus block. The frequency of the intervening stimulus varied between different blocks from 578 Hz to 1728 Hz and its location varied in parallel with the frequency along the left-right dimension through 7 different locations. The constant inter-stimulus interval was 460 msec. The EEG was recorded at Cz and Fz. The N1 wave elicited by the test stimuli was smaller the smaller was the separation between the two stimuli in frequency or location. These results were interpreted in terms of stimulus-specifically adapted detector activity. The more the test and intervening stimuli resemble each other the greater is the overlap between the respective feature-detector populations activated and, therefore, the smaller is the N1 amplitude. Thus the sensory-specific component of the N1 wave generated in the primary auditory areas at least in part reflects detector activity. The selective frequency adaptation was much more specific in the present study than in the previous ones and suggested that the N1 component recorded was generated by highly frequency-specific neurons. The frequency and location effects were independent, i.e., the frequency effect was rather similar for different location separations, and vice versa. Thus, evidence for separate detectors for frequency and location of an auditory stimulus was obtained.

Adult↗
PubMed1987

Brain mechanism of selective listening reflected by event-related potentials.

Stimulus selection during selective listening on the basis of simple physical stimulus features is reflected by an event-related potential (ERP) component called the processing negativity (PN). PN has been proposed to indicate a matching or comparison process between the physical features of the stimulus and an 'attentional trace,' an actively formed and maintained temporary neuronal representation of the features defining the relevant stimuli. According to this theory, the smaller is the difference between the eliciting stimulus and that represented by the attentional trace, the longer time is the stimulus processed, and thus the larger in amplitude and longer in duration is the PN elicited. The relevant stimuli, perfectly matching with the attentional trace, and therefore eliciting the largest and longest-duration PN, are selected for further processing. In the present study, the relevant and irrelevant stimuli differed in pitch, and the magnitude of this pitch separation was varied between different stimulus blocks. The results support the afore-mentioned matching or comparison hypothesis of selective attention by showing that PN is not elicited only by the relevant stimuli but even by irrelevant stimuli, and further that the latter PN is larger in amplitude and longer in duration the more similar the irrelevant stimuli are to the relevant stimuli. This PN, however, was smaller than that to the relevant stimuli even for very small separations, reflecting high accuracy of the discrimination function of the attentional trace mechanism proposed to underly selective listening. The termination of the PN to the irrelevant stimuli was followed by a positivity which thus partly explained the difference (Nd) between the ERPs to the relevant and irrelevant stimuli.

Adult↗
PubMed1987

Stimulus selection during auditory spatial attention as expressed by event-related potentials.

Selective listening to stimuli with certain physical features, such as pitch or location, is reflected by an event-related brain-potential (ERP) component called the processing negativity (PN). PN may reflect a matching or comparison process between the sensory inflow and the hypothesized 'attentional trace'. The latter is an actively formed and maintained neuronal representation of the physical features defining the relevant stimulus. According to this matching theory of selective attention, the better the sensory input corresponds to the attentional trace the longer the stimulus is processes (as reflected by a larger and longer PN). This theory is supported by the experiment in which the relevant and irrelevant stimuli were separated from one another in pitch. It was found that even the irrelevant stimuli elicited PN, and further that this PN was larger the smaller the pitch separation between the eliciting stimuli and the relevant stimuli. The largest PN was elicited by the relevant stimuli. The present study finds analogous results when the relevant and irrelevant stimuli are separated in spatial origin rather than in pitch.

Adult↗
PubMed1985

Auditory frequency discrimination and event-related potentials.

Auditory stimulus blocks were presented to 6 subjects. 80% of the stimuli in each block were standards of 1000 Hz and 20% were deviants of either 1002 Hz, 1004 Hz, 1008 Hz, 1016 Hz or 1032 Hz, one deviant type in each block. The constant interstimulus interval was 1 sec and the order of the stimuli was randomized. The subject was instructed either to ignore the deviant stimuli (ignore condition) or to press a response key to them (discrimination condition). In the ignore condition, an ERP component called the mismatch negativity (MMN), with a peak latency of approximately 170 msec, was elicited by those deviants exceeding the discrimination threshold (1016 Hz and 1032 Hz) and also those at the threshold (1008 Hz) tended to elicit a small MMN. In the discrimination condition, in addition to MMN, another negative component, N2b, was elicited by the detected deviants. This component had a somewhat longer latency than, and its midline distribution was posterior to, the MMN. The present results are in line with the hypothesis according to which the MMN component reflects the activation of cerebral mechanisms of passive discrimination, those which cause us to become aware of occasional changes in unattended stimulus sequences. In the discrimination condition, N2b and the slow parietal positivity were dominant features of the ERPs elicited by the detected suprathreshold deviants. The data obtained at the discrimination threshold specifically associate the parietal positivity with becoming aware of stimulus change since those deviants which were detected elicited this positivity whereas there was none to those (physically identical) deviants which remained undetected.

Acoustic Stimulation↗
PubMed1983

Sequential effects on the ERP in discriminating two stimuli.

Two auditory stimuli differing in pitch were presented in random order and equal probability with the constant inter-stimulus interval of 1 sec. The subject's task was to count one of these stimuli. The event-related brain potentials (ERPs) to each stimulus were averaged according to the immediately preceding stimulus sequence. It was found that when a few consecutive repetitions of one stimulus occurred, the ERP to the other stimulus immediately after those repetitions included features resembling those of the ERP to the infrequent stimulus usually observed in the so called 'oddball paradigm'. These features included, among other things, the mismatch negativity usually regarded as a scalp reflection of the neuronal mismatch process with an existing neuronal model. The mismatch negativity was accompanied by an 'N2b', a sharper and later negativity. Interestingly, N2b only occurred when the not-to-be-counted stimulus succeeded (one or several) counted stimuli but not when the order was reversed. This suggests that N2b reflects template mismatch, the occurrence of a stimulus mismatching with the mental image of the target stimulus voluntarily held by the subject.

Adult↗