Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Author: search.filters.author.Versnel, H.Subject: search.filters.subject.Communication

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    Comparison of Responses in the Anterior and Primary Auditory Fields of the Ferret Cortex
    (1994) Kowalski, Nina; Versnel, H.; Shamma, . S.A.; ISR
    Characteristics of an anterior auditory field (AAF) in the ferret auditory cortex are described in terms of its electrophysiological responses to tonal stimuli and compared to those of primary auditory cortex (AI). Units in both areas were presented with the same stimulus paradigms and their responses analyzed in the same manner so that a direct comparison of responses was possible. The AAF is located dorsal and rostral to AI on the ectosylvian gyrus and extends into the suprasylvian sulcus rostral to AI. The tonotopicity is organized with high frequencies at the top of the sulcus bordering the high- frequency area of AI, then reversing with lower BFs extending down into the sulcus. AAF contained single units that responded to a frequency range of 0.2 - 30 kHz. Stimuli consisted of single-tone bursts, two-tone bursts and frequency modulated (FM) stimuli swept in both directions at various rates. Best frequency (BF) range, rate-level functions at BF, directional sensitivity, and variation in asymmetries of response areas were all comparable characteristics between AAF and AI. The characteristics that were different between the two cortical areas were: latency to tone onset, excitatory bandwidth 20 dB above threshold (BW20) and preferred FM rate, as parameterized with the centroid (a weighted average of spike counts). The mean latency of AAF units was shorter than in AI (16.5 ms AAF, 19.4 ms AI). BW20 measurements in AAF were typically twice as large as those found in AI (2.5 oct AAF, 1.3 oct AI). There was a wider range of centroids found in AI than in AAF, and the relationships between BW20 and centroid were different for AAF and AI. The relationship between centroid and BW20 was examined to see if wider bandwidths were a factor in a unit's ability to detect fast sweeps. There was significant (P<0.05) linear correlation in AAF but not in AI. In both fields, the variance of the centroid population decreased with increasing BW20. BW20 decreased as BF increased for units in both auditory fields.
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    Ripple Analysis in Ferret Primary Auditory Cortex. II. Topographic and Columnar Distribution of Ripple Response Parameters
    (1994) Versnel, H.; Kowalski, Nina; Shamma, S.A.; ISR
    We examined the columnar and topographic distribution of response parameters using spectral ripples and tonal stimuli in the primary auditory cortex (AI) of the barbiturate-anesthetized ferret. The ripple stimuli consisted of broadband stimuli (1-20 kHz) with sinusoidally modulated spectral envelopes.

    Responses to ripples were parametrized in terms of characteristic ripple Wo(ripple frequency where the magnitude of the ripple transfer function is maximal, i.e., where the cell responds best) and characteristic phase Fo (intercept of the phase of the ripple transfer function, i.e., phase where the cell responds best). The response area (measured with tones) was parametrized in terms of its excitatory bandwidth at 20 dB above threshold (BW20), and its asymmetry as reflected by the directional sensitivity index (C) to frequency-modulated (FM) tones. Columnar organization for the above four parameters was investigated in 66 single units from 23 penetrations. It was confirmed for Wo, Fo, and the C index, but it appeared to be ambiguous for BW20. The response parameters measured from multiunit recordings corresponded closely to those obtained from single units in the same cluster. In a local region, most cells exhibited closely matched, response fields (RFs, inverse Fourier transformed ripple transfer function) and response areas (measured with two-tone stimuli), and had correspondingly similar response parameters to ripples and tones. The topographic distribution of the response parameters across the surface of AI was studied with multiunit recordings in four animals. In all maps, systematic patterns or clustering of, response parameters could be discerned along the isofrequency planes.

    The distribution of the characteristic ripple Wo exhibited two trends. First, along the isofrequency planes, it was largest near the center of AI, gradually decreasing towards the edges of the field where often a secondary maximum was found.

    The second trend occurred along the tonotopic axis where the maximum Wo found in an isofrequency range increases with increasing BF. The tonal bandwidth BW20, which was inversely correlated with Wo, exhibited a similar topographic distribution along the tonotopic axis and the isofrequency planes. The distribution of the characteristic ripple phase, Fo which reflects the asymmetry in the response field, showed a systematic order along the isofrequency axis. At the center of AI symmetric responses (Fo 0) predominated. Towards the edges, the RFs became more asymmetric with Fo < 0 caudally, and Fo > 0 rostrally. The asymmetric response types tended to cluster along repeated bands that paralleled the tonotopic axis. The FM directional sensitivity (C index, reflecting asymmetry of tonal response areas) tends to have similar trends along the isofrequency axis as Fo.