Effect of frequency separation and stimulus rate on the mismatch negativity: an examination of the issue of refractoriness in humans.

Refractoriness of the generators of the mismatch negativity (MMN) was examined in two experiments in which two deviant tones occurred in a row. In Experiment 1, the size of the MMN elicited by the first deviant was manipulated by using deviants that were close to or far from the standard in frequency. In Experiment 2, the time between two identical deviants was varied. It was found that neither the size of the MMN elicited by the first deviant, nor the time between two deviants, affected the amplitude of the MMN elicited by the second deviant. It was concluded that refractoriness played no role in the amplitude of the MMN for the parameters used.

Feature conjunctions and auditory sensory memory.

This study sought to obtain additional evidence that transient auditory memory stores information about conjunctions of features on an automatic basis. The mismatch negativity of event-related potentials was employed because its operations are based on information that is stored in transient auditory memory. The mismatch negativity was found to be elicited by a tone that differed from standard tones in a combination of its perceived location and frequency. The result lends further support to the hypothesis that the system upon which the mismatch negativity relies processes stimuli in an holistic manner.

Automatic change detection: does the auditory system use representations of individual stimulus features or gestalts?

The effects of global and feature-specific probabilities of auditory stimuli were manipulated to determine their effects on the mismatch negativity (MMN) of the human event-related potential. The question of interest was whether the automatic comparison of stimuli indexed by the MMN was performed on representations of individual stimulus features or on gestalt representations of their combined attributes. The design of the study was such that both feature and gestalt representations could have been available to the comparator mechanism generating the MMN. The data were consistent with the interpretation that the MMN was generated following an analysis of stimulus features.

Storage of information in transient auditory memory.

This study concerns the manner in which features of auditory stimuli are stored in acoustic memory. Event-related potentials (ERPs) were recorded to sequences of tones in which sequential, infrequent deviant tones were presented in a row, each of which differed from the frequent standard tones along a different stimulus dimension. The object was to determine whether a change in a single feature of a stimulus would have an effect on the entire representation of the standard tone in memory, or only on the representation of the stimulus dimension by which the first deviant differed from the standards. It was found that the amplitude of the mismatch negativity elicited by subsequent deviants was not reduced by the presence of the first deviant, supporting independent storage of features.

Variation in the latencies and amplitudes of N400 and NA as a function of semantic priming.

The purpose of this study was to determine whether the latencies of two event-related potential (ERP) components, the NA and N400, were sensitive to semantic priming. Subjects performed a semantic judgment task, which was designed in such a way that the N400 could be examined without overlap from the P3. Priming effects on the latencies of both NA and N400 were most apparent at frontocentral sites. The amplitude of NA was not significantly affected by priming. The amplitude of N400 was smaller for primed than for unprimed words, but the effect was significant only at centroposterior sites. Current source density (CSD) analyses performed on the ERP data suggested the activation of multiple generators in the N400 time region. The ERP and CSD data were consistent with the existence of two types of N400, a frontal N400 that varies in latency as a function of semantic priming, and a posterior N400 that varies in amplitude.

Frequency specificity of the auditory brain stem response to bone-conducted tones in infants and adults.

Auditory brain stem responses were obtained from normal-hearing infants and adults in response to bone-conducted 500 and 2000 Hz tones presented in quiet and high-pass noise masking. The tones were presented at 70 (500 and 2000 Hz) and 46 (2000 Hz) dB peak to peak equivalent (re: 1 dyne RMS). The high-pass noise-masked waveforms were subtracted in succession to obtain derived responses, providing estimates of the cochlear regions contributing to the nonmasked responses. Findings indicate that the auditory brain stem response to bone-conducted 500 Hz tones is frequency specific for both infants and adults. For 2000 Hz tones, the results show maximum amplitudes for cochlear regions representing the nominal frequency of the tone for adults. For infants, maximum response amplitudes for the derived responses to 2000 Hz, 70 dB tones were obtained within 1/2 octave of the nominal frequency (1410-2000 Hz). Wave V latencies of the derived responses are similar for both groups for 2000 Hz tones, but shorter for infants to 500 Hz tones, supporting the hypothesis that low-frequency bone-conducted stimuli are effectively more intense in infants than adults.