Biomedical subjects

I Nimmo-Smith

Publications and source records attributed to I Nimmo-Smith.

23 records · Page 2Linked to original sources

PubMed1984

Dynamic range and asymmetry of the auditory filter.

This experiment was designed to measure the shape and asymmetry of the auditory filter over a wider dynamic range than has been measured previously. Thresholds were measured for 2-kHz sinusoidal signals in the presence of two 800-Hz-wide noise bands, one above and one below the signal frequency. The spectrum level of the noise was 45 dB (re: 20 muPa), and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the signal frequency from the nearer edge of each noise band varied from 0 to 0.8 times the signal frequency. Each ear of six subjects was tested, and the subjects' ages ranged from 22 to 74 years. The auditory filters derived from the data were somewhat asymmetric, with steeper slopes on the high-frequency side; the degree of asymmetry varied across subjects. The asymmetry could be characterized as a uniform stretching of the (linear) frequency scale on one side of the filter. The dynamic range of the auditory filter exceeded 60 dB in the younger listeners, but the dynamic range and sharpness of the filter tended to decrease with increasing age.

Adult↗

PubMed1984

On the reduction of eye-strain when reading.

Successive lines of printed text form a pattern of stripes that may induce eye-strain and headache. Volunteers suffering eye-strain or headache from reading were asked to use a variety of aids, some of which merely guided the eye and some of which also attenuated the pattern of stripes above and below the passage of text being read. In two studies about one-third of the volunteers benefited from the latter acids to the extent that they wished to continue using them despite the inconvenience involved. These volunteers tended to report more visual illusions when they looked at a pattern of striped lines.

Adult↗

PubMed1982

"Outcome-counting'-Significance tests from incomplete predictions of order.

Experiments testing models usually predict that some treatment effects will be greater than others, but they do not as a rule feel able to predict the exact ordering of treatment effects. A useful significance test for such incomplete order predictions can be obtained by comparing the number of possible outcomes (orderings) with the number that satisfy the predictions. The difficulty is to count the outcomes satisfying the predictions, which can be a lengthy task if there are many treatments. A straightforward method of outcome-counting is derived from simple algebra and examples of its use are given.

Humans↗

PubMed1982

The deterioration of hearing with age: frequency selectivity, the critical ratio, the audiogram, and speech threshold.

The frequency selectivity of the auditory system was measured by masking a sinusoidal signal (0.5, 2.0, or 4.0 kHz) or a filtered-speech signal with a wideband noise having a notch, or stopband, centered on the signal. As the notch was widened performance improved for both types of signal but the rate of improvement decreased as the age of the 16 listeners increased from 23 to 75 years, indicating a loss in frequency selectivity with age. Auditory filter shapes derived from the tone-in-noise data show (a) that the passband of the filter broadens progressively with age, and (b) that the dynamic range of the filter ages like the audiogram. That is, the range changes little with age before 55, but beyond this point there is an accelerating rate of loss. The speech experiment shows comparable but smaller effects. The filter-width measurements show that the critical ratio is a poor estimator of frequency selectivity because it confounds the tuning of the system with the efficiency of the signal-detection and speech-processing mechanisms that follow the filter. An alternative, one-point measure of frequency selectivity, which is both sensitive and reliable, is developed via the filter-shape model of masking.

Adult↗

PubMed1980

Off-frequency listening and auditory-filter asymmetry.

The phenomenon of off-frequency listening, and the asymmetry of the auditory filter, were investigated by performing a masking experiment in which a 2.0-kHz tonal signal (0.4 sec in duration) was masked by a pair of noise bands, one below and the other above the tone. The noise bands were 0.8-hKz wide. The edges of the bands were very sharp, the spectrum level in the band was 40 dB SPL, and the masker was on continuously throughout the experiment. Tone threshold was measured as a function of the distances from the tone to the nearer edge of each noise band. It was assumed that conditions in which one noise band was near the tone and the other remote from the tone would encourage the observer to listen off frequency, that is, to center his auditory filter, not at the tone frequency, but at the frequency that optimizes the signal-to-noise ratio at the output of the filter. The threshold data were analysed with a power spectrum model of masking in which it was assumed that the general form of the filter shape was a rounded exponential (a pair of back-to-back, negative exponentials with the peak smoothed and the tails raised). The specific filter shape obtained by applying this model to the threshold data has a broad passband (a 200-Hz, 3-dB bandwidth), steep skirts (slopes of 100 dB/octave) and shallower tails (slopes of 30-50 dB/octave) that take over 30-35 dB down from the peak of sensitivity. The filter is asymmetric, with the lower branch slightly broader than the upper. The filter is shifted off frequency by more than half its bandwidth in some cases, and the shift can improve the signal-to-noise ratio by up to 5.0 dB.

Auditory Threshold↗