The effect of sensorineural hearing loss on suprathreshold perception of tonal components in noise.

The present study investigates how sensorineural hearing loss affects the perception of suprathreshold tonal components in noise. Masked threshold, tonality, and loudness of the tonal content are measured for one, two, or four simultaneously presented sinusoids. The levels of the suprathreshold tonal components were chosen relative to the individual masked thresholds. Masked thresholds were significantly higher for the hearing-impaired listeners than for normal-hearing listeners. In general, tonality was the same for hearing-impaired and normal-hearing listeners at the same level above threshold. The same was found for the loudness of the tonal content.

Temporal loudness weights: Primacy effects, loudness dominance and their interaction.

Loudness judgments of sounds varying in level across time show a non-uniform temporal weighting, with increased weights assigned to the beginning of the sound (primacy effect). In addition, higher weights are observed for temporal components that are higher in level than the remaining components (loudness dominance). In three experiments, sounds consisting of 100- or 475-ms Gaussian wideband noise segments with random level variations were presented and either none, the first, or a central temporal segment was amplified or attenuated. In Experiment 1, the sounds consisted of four 100-ms segments that were separated by 500-ms gaps. Previous experiments did not show a primacy effect in such a condition. In Experiment 2, four- or ten-100-ms-segment sounds without gaps between the segments were presented to examine the interaction between the primacy effect and level dominance. As expected, for the sounds with segments separated by gaps, no primacy effect was observed, but weights on amplified segments were increased and weights on attenuated segments were decreased. For the sounds with contiguous segments, a primacy effect as well as effects of relative level (similar to those in Experiment 1) were found. For attenuation, the data indicated no substantial interaction between the primacy effect and loudness dominance, whereas for amplification an interaction was present. In Experiment 3, sounds consisting of either four contiguous 100-ms or 475-ms segments, or four 100-ms segments separated by 500-ms gaps were presented. Effects of relative level were more pronounced for the contiguous sounds. Across all three experiments, the effects of relative level were more pronounced for attenuation. In addition, the effects of relative level showed a dependence on the position of the change in level, with opposite direction for attenuation compared to amplification. Some of the results are in accordance with explanations based on masking effects on auditory intensity resolution.

Temporal Loudness Weights Are Frequency Specific.

Previous work showed that the beginning of a sound is more important for the perception of loudness than later parts. When a short silent gap of sufficient duration is inserted into a sound, this primacy effect reoccurs in the second sound part after the gap. The present study investigates whether this temporal weighting occurs independently for different frequency bands. Sounds consisting of two bandpass noises were presented in four different conditions: (1) a simultaneous gap in both bands, (2) a gap in only the lower frequency band, (3) a gap in only the higher frequency band, or (4) no gap. In all conditions, the temporal loudness weights showed a primacy effect at sound onset. For the frequency bands without a gap, the temporal weights decreased gradually across time, regardless of whether the other frequency band did or did not contain a gap. When a frequency band contained a gap, the weight at the onset of this band after the gap was increased. This reoccurrence of the primacy effect following the gap was again largely independent of whether or not the other band contained a gap. Thus, the results indicate that the temporal loudness weights are frequency specific.

The effect of silent gaps on temporal weights in loudness judgments.

Human loudness judgments of time-varying sounds show a non-uniform temporal weighting pattern with increased weights at the beginning of a sound. Four experiments were conducted to investigate whether this primacy effect reoccurs after a silent gap of an appropriate duration that is inserted into a level-fluctuating sound. In three of the experiments, contiguous sounds as well as sounds containing silent gaps of different durations were presented. The temporal loudness weights were compared between the sounds that contained a gap and the sounds without a gap. The data showed that with increasing gap duration an increasingly pronounced primacy effect reoccurred on the second sound part in the sense that a) the weights assigned to the first segments after the gap were increased compared to the conditions without a gap, and that b) the following weights again showed a decrease over time. This effect was statistically significant for gap durations of 350 ms and above. To investigate whether an attenuation in level can lead to the same results as a silent gap, segments in the middle part of a sound were attenuated in the fourth experiment, and the resulting weights were compared to conditions in which the middle segments were unattenuated or where a 700 ms silent gap was presented instead of the middle segments. An attenuation of 15 dB resulted in a significant reoccurrence of the primacy effect, although the effect was more pronounced for an attenuation of 30 dB and the silent gap. The results are discussed in the light of auditory nerve responses, masking effects on intensity resolution, and assumptions based on evidence integration processes.

Temporal weights in loudness: Investigation of the effects of background noise and sound level.

Previous research has consistently shown that for sounds varying in intensity over time, the beginning of the sound is of higher importance for the perception of loudness than later parts (primacy effect). However, in all previous studies, the target sounds were presented in quiet, and at a fixed average sound level. In the present study, temporal loudness weights for a time-varying narrowband noise were investigated in the presence of a continuous bandpass-filtered background noise and the average sound levels of the target stimuli were varied across a range of 60 dB. Pronounced primacy effects were observed in all conditions and there were no significant differences between the temporal weights observed in the conditions in quiet and in background noise. Within the conditions in background noise, there was a significant effect of the sound level on the pattern of weights, which was mainly caused by a slight trend for increased weights at the end of the sounds ("recency effect") in the condition with lower average level. No such effect was observed for the in-quiet conditions. Taken together, the observed primacy effect is largely independent of masking as well as of sound level. Compatible with this conclusion, the observed primacy effects in quiet and in background noise can be well described by an exponential decay function using parameters based on previous studies. Simulations using a model for the partial loudness of time-varying sounds in background noise showed that the model does not predict the observed temporal loudness weights.

Evaluation of a model of temporal weights in loudness judgments.

The onset of a sound receives a higher weight than later portions in time when its loudness is assessed, an effect commonly referred to as primacy effect. It is investigated if this effect can be predicted on the basis of an exponentially decaying function where the weight assigned to a temporal portion of a sound is the integral of this function over the segment duration. To test this model, temporal loudness weights were measured for sounds with different segment durations and total durations. The model successfully predicted essential aspects of the data.

On the Pitch Strength of Bandpass Noise in Normal-Hearing and Hearing-Impaired Listeners.

The psychoacoustic measure pitch strength describes the strength of the tonal sensation evoked by a sound on a scale from weak to strong. For normal-hearing listeners, it was shown in the literature that pitch strength of bandpass noise (relative to the pitch strength of a sinusoid at its center frequency) decreases with increasing bandwidth. This decrease also depends on the center frequency. These effects were often attributed to the frequency selectivity of the auditory system. The present study investigated the relative pitch strength of bandpass noise in hearing-impaired listeners and for comparison in a normal-hearing control group. For the normal-hearing listeners, pitch strength was measured at sound pressure levels of 30 and 70 dB SPL for bandwidths between 5 and 1620 Hz and center frequencies of 375, 750, and 1500 Hz. In addition, two ways of generating the stimuli (filtering in frequency or time domain) were used to compare the data with previous results. Apart from the known effect of center frequency on the change of relative pitch strength with increasing bandwidth, stimulus generation also had a significant influence on the results. Relative pitch strength of bandpass noise in hearing-impaired listeners was measured for bandwidths from 5 to 1620 Hz; the center frequency was 1500 Hz. Compared with the corresponding results of the normal hearing, relative pitch strength was altered in the hearing-impaired listeners. These alterations, however, could not be explained by altered spectral processing in the damaged cochlea alone.

Temporal weights in the perception of sound intensity: Effects of sound duration and number of temporal segments.

Loudness is a fundamental aspect of auditory perception that is closely related to the physical level of the sound. However, it has been demonstrated that, in contrast to a sound level meter, human listeners do not weight all temporal segments of a sound equally. Instead, the beginning of a sound is more important for loudness estimation than later temporal portions. The present study investigates the mechanism underlying this primacy effect by varying the number of equal-duration temporal segments (5 and 20) and the total duration of the sound (1.0 to 10.0 s) in a factorial design. Pronounced primacy effects were observed for all 20-segment sounds. The temporal weights for the five-segment sounds are similar to those for the 20-segment sounds when the weights of the segments covering the same temporal range as a segment of the five-segment sounds are averaged. The primacy effect can be described by an exponential decay function with a time constant of about 200 ms. Thus, the temporal weight assigned to a specific temporal portion of a sound is determined by the time delay between sound onset and segment onset rather than by the number of segments or the total duration of the sound.

Mid-bandwidth loudness depression in hearing-impaired listeners.

The loudness of a bandpass-filtered noise depends on its bandwidth. For bandwidths larger than a critical bandwidth, loudness increases as the bandwidth increases, an effect commonly referred to as spectral loudness summation. For bandwidths smaller than the critical bandwidth, it was shown recently for normal-hearing listeners that loudness decreases as the bandwidth increases. This study investigated if listeners with a hearing impairment of primarily cochlear origin also showed this effect. Levels at equal loudness between a 1500-Hz pure-tone reference and noise-band targets centered at 1500 Hz were measured for bandwidths in the range from 15 to 1620 Hz. The reference level was adjusted individually on the basis of the audiogram. The average level difference at equal loudness increased from 0 dB at 15 Hz up to a maximum of about 4 dB at 810 Hz. Thus, the mid-bandwidth loudness depression is also observed for hearing-impaired listeners.