G. Bruce Henning

Detectability of interaural delay in high‐frequency complex waveforms

Observers can detect interaural delays in three component stimuli produced by sinusoidally modulating the amplitude of a sinusoidal carrier. Interaural delays are detected in stimuli confined to a high‐frequency region even in the presence of an intense, low‐pass filtered noise. With 300‐Hz modulation of a 3900‐Hz carrier, detection of interaural delay is equally good when either the entire stimulus or just the envelope of the stimulus is delayed. In either case performance is as good as with a 300‐Hz pure tone.

Some experiments bearing on the hypothesis that the visual system analyses spatial patterns in independent bands of spatial frequency

Abstract Gratings with three sinusoidal components of high spatial frequency are shown to interact with a sinusoidal grating two octaves lower in frequency. This finding is inconsistent with the hypothesis that the visual system analyses spatial patterns in independent narrowly-tuned bands of spatial frequency.

Effects of different hypothetical detection mechanisms on the shape of spatial-frequency filters inferred from masking experiments: I. noise masks

The detectability of a sinusoidal grating was measured in a standard two-interval forced-choice experiment against backgrounds of noise gratings of the same orientation as the signal. The noise gratings were either spatially high-pass or low-pass filtered and were either unchanged in each observation interval (static) or flickering at a rate that depended on their cutoff frequency (dynamic). Spatial-frequency-selective mechanisms are inferred from the data and their characteristics shown to depend on assumptions concerning the detection process thought to follow the spatial-frequency-selective device.

Stimulus variability and auditory filter shape

We have investigated the way in which stimulus variability will affects the attenuation characteristic or auditory filter shape inferred from masking experiments. Stimulus variability was found to have a pronounced effect on filter shapes derived from bandlimiting experiments in which the signal is a tone, the masker is a band of noise centered on the tone, and the independent variable is the width of the noise band. But stimulus variability had virtually no effect on filters obtained from notched noise masking experiments. In an attempt to extend the utility of the filter‐shape concept we have replicated an earlier experiment in which the masker is two tones rather than noise. The tones, each 57 dB SPL, were used to mask a narrow band of noise centered midway between them and threshold for the noise signal was measured as a function of the frequency separation of the tonal maskers. The form of the data is in good agreement with the auditory filter shape derived using a notched‐noise masker and a tonal si...

SOME OBSERVATIONS ON THE MASKING EFFECTS OF TWO-DIMENSIONAL STIMULI

Gratings that differ in orientation by as much as 62.5 deg from that of a signal grating raise the signals threshold by nearly a log unit. The spatial-frequency tuning of the masking effect reaches a maximum slightly below the spatial frequency of the maskers but far from that of any quadratic distortion product. Further, the location of the peak does not depend much on the relative orientation of the signal and maskers thus making it unlikely that the masking effect can be explained in any simple way by the presence of visual nonlinearities. This illustrates the difficulty of attempting to explain human performance in even relatively simple discrimination experiments with models based on mechanisms tuned for spatial frequency and orientation.

Effect of interaural phase on frequency and amplitude discrimination

The resolution of frequency and amplitude is better at low signal‐to‐noise ratios with out‐of‐phase signals than with in‐phase signals when the noise in which the signals are presented is the same at both ears. On the other hand, at high signal‐to‐noise ratios, the effects of the interaural phase of the signals are negligible. These findings are discussed in terms of the predictions of a modified version of Durlachs Equalization and Cancellation Model and the Webster‐Jeffress Model of the binaural masking level difference.

A neurophysiologically plausible population-code model for human contrast discrimination

The pedestal effect is the improvement in the detectability of a sinusoidal grating in the presence of another grating of the same orientation, spatial frequency, and phase-usually called the pedestal. Recent evidence has demonstrated that the pedestal effect is differently modified by spectrally flat and notch-filtered noise: The pedestal effect is reduced in flat noise but virtually disappears in the presence of notched noise (G. B. Henning & F. A. Wichmann, 2007). Here we consider a network consisting of units whose contrast response functions resemble those of the cortical cells believed to underlie human pattern vision and demonstrate that, when the outputs of multiple units are combined by simple weighted summation-a heuristic decision rule that resembles optimal information combination and produces a contrast-dependent weighting profile-the network produces contrast-discrimination data consistent with psychophysical observations: The pedestal effect is present without noise, reduced in broadband noise, but almost disappears in notched noise. These findings follow naturally from the normalization model of simple cells in primary visual cortex, followed by response-based pooling, and suggest that in processing even low-contrast sinusoidal gratings, the visual system may combine information across neurons tuned to different spatial frequencies and orientations.

The effect of carrier and modulation frequency on lateralization based on interaural phase and interaural group delay

The sensitivity of Observers to interaural delay in either the envelope or the carrier of an amplitude-modulated sinusoid was measured in a two-interval forced-choice task as a function of the frequency of the modulation and the frequency of the carrier. The two types of delay were set in opposition with the carrier leading in one ear but the modulation leading in the other. Lateralization appeared to be based on carrier (phase) delay when carrier frequency was below 1500 Hz, whatever the modulation frequency. For carrier frequency greater than 1500 Hz, lateralization performance was dependent both on carrier and on modulation frequency and was based on modulation (group) delay.

Lateralization and the binaural masking‐level difference

Observers can readily detect interaural delays in certain complex waveforms even when the energy in the waveform is confined to high‐frequency regions. However, the detectability of such complex waveforms is not measurably dependent on interaural phase—that is, there is no masking‐level difference with high‐frequency signals in spite of the fact that interaural phase effects are readily observed as changes in the apparent location of the source of the signal.

Lateralization of low-frequency transients ☆

Abstract Lateralization experiments with several types of interaural delay in transient signals of low frequency extend the observations on lateralization of three tone complexes and indicate that observers are insensitive to interaural group delay in low-frequency transients.