Deficits In Temporal Resolution Research Articles

Temporal resolution deficits in the visual fields of MS patients

We assessed the relationship between temporal resolution and MS-induced neuropathy. A diagnostic strategy comprising assessments of temporal resolution at 16 points in the extra-foveal visual field up to 12° from the fovea was first compared with foveal temporal resolution and with a standard VEP procedure in the same MS patients. At the group level, foveal temporal resolution was less sensitive to demyelination than the 16-point diagnostic strategy, the detection rate of which was comparable to that of the VEP procedure. Cross-sensitivity of the VEP and the 16-point diagnostic procedure was low. Subsequently, the average severity of MS-induced temporal resolution deficits was studied at three retinal loci of the same size but different eccentricities. Foveal deficits were not significantly greater than more peripheral deficits within the central 12°.

Use of temporal information in recognition of amplitude-compressed speech by older adults

Amplitude compression alters the speech envelope and under some conditions can reduce the availability of temporal cues for speech recognition. This may be a particular problem for older listeners, who demonstrated temporal resolution deficits in some studies. Older and younger hearing-impaired listeners were tested on their recognition of VCV syllables processed using the signal-correlated noise (SCN) method [Schroeder, J. Acoust. Soc. Am. 44, 1735–1736 (1968)]. This method results in a time-varying speech envelope modulating a noise carrier, and preserves temporal cues while minimizing spectral information. Recognition scores were obtained for uncompressed SCN syllables and for the same speech tokens after digital processing with a syllabic compression algorithm. In control conditions, recognition was tested for VCVs that included both temporal and spectral information. Younger and older listener groups were matched for mean hearing thresholds up to 4 kHz. A high-pass masker was included to eliminate contributions from the basal end of the cochlea. When compared to younger listeners with similar hearing losses, the older listeners demonstrated poorer performance on the compressed SCN signals. These results suggest that the poorer temporal resolution abilities of older listeners may play a role in their understanding of amplitude-compressed speech.

Neural processing of temporal gaps in the inferior colliculus of the awake young and old CBA mouse

The ability to detect brief silent intervals or gaps in sound forms one important property of temporal resolution. Psychoacoustical evidence suggests such fundamental processing correlates with more complex perceptions, such as speech perception in noise. Moreover, studies have also implicated deficits in temporal resolution as a possible cause for the difficulties observed in presbycusis. The current study compared neuronal response properties and minimal gap thresholds (MGT) in the young (2–4 month) and old (≳24 month) CBA mouse model of presbycusis. The following measures were obtained from over 40 single units in each age group; intensity functions for 100-ms tone and noise bursts, spontaneous rate, Q10 bandwidth, and gap functions. Neural correlates of gap detection were studied by imbedding a silent gap (widths from 0.5 to 20 ms) between two noise bursts presented at 30 dB above unit threshold. MGT was quantified by comparing spike counts in multiple time windows before, during, and after the gap. Comparison between young and old response patterns indicate: (1) PST histograms displayed numerous patterns including; onset, onset-sustained, on-off, primarylike, buildup, and off responses, (2) a wide range of spontaneous rates were encountered from 0 to 60 spikes/s, (3) MGT varied with response type regardless of age, and (4) the lowest MGTs (1–2 ms) observed were found both in young and old animals, but the frequency of occurrence was lower in the older animals. [Work supported by NIH-NIA P01 AG09524-01A1.]

Monotic and dichotic fusion thresholds in patients with unilateral subcortical lesions

Tone gap detection thresholds under conditions of monotic and dichotic mode were measured from the three groups of subjects; patients with right subcortical lesions, patients with left subcortical lesions and normal individuals. A significant difference of the thresholds among the three groups was observed in the dichotic condition but not in the monotic condition. The patients with right subcortical lesions showed a gross deficit in temporal resolution even when the stimuli were presented dichotically. The results are discussed in relation to functional differentiation of right and left subcortical structures for temporal processing.