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J Mertus

Publications and source records attributed to J Mertus.

3 recordsLinked to original sources
PubMed1986

Methods for the identification of evoked response components in the frequency and combined time/frequency domains.

Two prominent frequency components designated f1 and f2 have been identified in the visual evoked response to the transient presentation of sinusoidal luminance gratings in the range of 0.5-8 c/deg. The components occur at temporal frequencies below the alpha band, with the f1 frequency being roughly half that of the f2 frequency. The f1 component is largest at low spatial frequencies with f2 becoming progressively dominant as spatial frequency is increased. The frequency and amplitude of f1 and f2 change substantially over the time course of the response. This has been studied by calculating the temporal frequency spectrum of the transient evoked potential over successive short-time epochs running through the response. Using this technique, the response is shown to consist of narrow-band frequency peaks or 'formants' emerging at different times after stimulus onset. These formants occur at frequencies other than those of the spontaneous EEG and undergo changes in frequency and amplitude over the time course of the response. Two spectrum analysis techniques were employed: the Discrete Fourier Transform and Linear Predictive Coding. Frequency components were successfully identified in single-trial responses using the LPC technique.

Electroencephalography↗
PubMed1982

The role of the gross spectral shape as a perceptual cue to place articulation in initial stop consonants.

This series of studies explored the extent to which the gross shape of the onset spectrum is used by the listener for the identification of place of articulation in initial stop consonants. Synthetic stimuli were generated with onset frequencies appropriate to the syllables [ba bi du da di du] and with the gross shape of the onset spectrum manipulated to be appropriate for either alveolar consonants or labial consonants. Stimuli were presented for identification and discrimination. In addition, adaptation effects of stimuli containing appropriate frequency and shape and incompatible frequency and shape were explored on a place-of-articulation onset continuum. Although identification performance was determined by onset frequency rather than gross shape of the spectrum, presentation of stimuli in which shape was inconsistent with frequency reduced identification performance. Further, subjects could discriminate stimuli which varied only in spectral shape. Finally, significantly less adaptation was found for a [da] onset with a labial spectrum shape than [da] onset with an alveolar spectrum shape. These results suggest that although the invariant properties residing in the gross shape of the onset spectrum may serve as a classificatory framework for the phonetic dimensions of natural language, they may not provide the primary perceptual attributes for place of articulation in ongoing speech processing.

Humans↗