An Adaptive Bias in the Perception of Looming Auditory Motion

Rising acoustic intensity can indicate movement of a sound source toward a listener. Perceptual overestimation of intensity change could provide a selective advantage by indicating that the source is closer than it actually is, providing a better opportunity for the listener to prepare for the source's arrival. In Experiment 1, listeners heard equivalent rising and falling level sounds and indicated whether one demonstrated a greater change in loudness than the other. In 2 subsequent experiments listeners heard equivalent approaching and receding sounds and indicated perceived starting and stopping points of the auditory motion. Results indicate that rising intensity changed in loudness more than equivalent falling intensity, and approaching sounds were perceived as starting and stopping closer than equidistant receding sounds. Both effects were greater for tones than for noise. Evidence is presented that suggests that an asymmetry in the neural coding of egocentric auditory motion is an adaptation that provides advanced warning of looming acoustic sources.     

Intensity discrimination and loudness for tones in broadband noise

In two previous papers (Parker & Schneider, 1980; Schneider & Parker, 1987), we developed a model, based on Fechner's assumption, which successfully predicted the relationship between loudness and intensity discrimination for tones presented in quiet and in notched noise. In the present paper, pure-tone intensity-increment thresholds and loudness matches were determined for several levels of a standard tone in the presence of a broadband masker whose spectrum level was set to 35 dB below that of the standard tone. The model was unable to relate loudness to intensity discrimination under these conditions. Thus, the spectral composition of the masker affects the relationship between loudness and intensity discrimination in ways that cannot be accounted for by the model.     

Continuous judgment of level-fluctuating sounds and the relationship between overall loudness and instantaneous loudness

Summary The present investigation was designed to examine the most appropriate duration of instantaneous loudness and to find out the relationship between overall loudness and instantaneous loudness using 20-min road traffic noise. Instantaneous loudness was judged using the method of continuous judgment by category. The results suggest that instantaneous loudness is determined by the sound energy averaged during the 2.5-s period preceding each judgment, the duration of which seems to reflect the psychological present. It was also found that overall loudess is not an average of the instantaneous loudness of every moment, but that it is based on the instantaneous loudness above a certain level.     

Binaural summation of loudness: Noise and two-tone complexes

A series of six experiments used the method of magnitude estimation to assess how the two ears sum the loudness of stimuli with various spectra. The results showed that the binaural system sums loudnesses by at least two distinct sets of rules, one applicable to narrow-band stimuli (complete loudness summation), another to wide-band noises (partial summation, dependent on level). The main findings were: (1) Narrow-band noise (Vi-octave bands at 1,000 Hz) showed complete binaural loudness summation, like that previously reported for pure tones (Marks, 1978a). At all but low SPL, a monaural stimulus must be 10 dB greater than a binaural stimulus to be equally loud; a stimulus ratio of 10 dB corresponds to a loudness ratio of 2:1 on Stevens’ sone scale. (2) Wide-band noise (300-4,800 Hz) showed only partial summation, the subadditivity being confined largely to levels below about 60 dB SPL. This result obtained both with bands of white noise (flat spectrum) and pink noise (—3 dB/ octave). (3) Binaural summation of two-tone complexes depended slightly on frequency spacing. Narrow spacing (860 and 1,160 Hz) gave summation equal to about 10 dB, like that of narrowband noises and single tones, whereas wider spacing (675 and 1,475 Hz) gave less summation, equal to about 9 dB, and more like wide-band noise; however, a very wide spacing (300 and 4,800 Hz) gave summation like that of narrow-band noises and single pure tones.     

Vibrotactile loudness addition

Os adjusted the intensity of vibration at a single locus on the right hand to a value equal in vibratory loudness to various patterns of vibration on the left hand. The patterns were created by 1 to 5 equated vibration generators, varied with respect to sensation level and distances among the vibrators. The results were: (a) increasing from 1 to 5 vibrators produced a doubling in vibratory loudness, (b) neither loudness level of the components nor distance among vibrators had any effect on the slope of the overall loudness growth function. as also adjusted the intensity of a white noise to equal in magnitude the patterns of vibration presented (a) to the left hand as before and (b) to loci distributed over the surface of the body. The results were the same as those obtained using a single vibrator as standard. The specific loci stimulated did not appear to have any effect on vibrotactile loudness addition.     

Vibrotactile loudness addition

Os adjusted the intensity of vibration at a single locus on the right hand to a value equal in vibratory loudness to various patterns of vibration on the left hand. The patterns were created by 1 to 5 equated vibration generators, varied with respect to sensation level and distances among the vibrators. The results were: (a) increasing from 1 to 5 vibrators produced a doubling in vibratory loudness, (b) neither loudness level of the components nor distance among vibrators had any effect on the slope of the overall loudness growth function. Os also adjusted the intensity of a white noise to equal in magnitude the patterns of vibration presented (a) to the left hand as before and(b) to loci distributed over the surface of the body. The results were the same as those obtained using a single vibrator as standard. The specific loci stimulated did not appear to have any effect on vibrotactile loudness addition.     

Spectral content as a cue to perceived auditory distance.

Changes in the spectral content of wide-band auditory stimuli have been repeatedly implicated as a possible cue to the distance of a sound source. Few of the previous studies of this factor, however, have considered whether the cue provided by spectral content serves as an absolute or a relative cue. That is, can differences in spectral content indicate systematic differences in distance even on their first presentation to a listener, or must the listener be able to compare sounds with one another in order to perceive some change in their distances? An attempt to answer this question and simultaneously to evaluate the possibly confounding influence of changes in the sound level and/or the loudness of the stimuli are described in this paper. The results indicate that a decrease in high-frequency content (as might physically be produced by passage through a greater amount of air) can lead to increases in perceived auditory distance, but only when compared with similar sounds having a somewhat different high-frequency content, ie spectral information can serve as a relative cue for auditory distance, independent of changes in overall sound level.     

Individual brightness functions

A total of 34 individual brightness functions were measured for 18 observers by two different methods. In one method the observer set various luminance levels of a white target and assigned numbers proportional to the apparent brightness of the levels set. In the other method the observer adjusted the loudness of a white noise and the luminance of a white target in order to achieve a series of cross-modality matches between loudness and brightness. Both methods gave good approximations to power functions, showing that the psychophysical power law holds for the individual perceiver.     

Binaural and temporal integration of the loudness of tones and noises

Subjects judged the loudness of tones (Experiment 1) and of bursts of noise (Experiment 2) that varied in intensity and duration as well as in mode of presentation (monaural vs. binaural). Both monaural and binaural loudness, for both types of signals, obeyed the bilinear-interaction prediction of the classic temporal integration model. The loudness of short tones grows as a power function of both intensity and duration with different exponents for the two factors (.2 and .3, respectively). The loudness of wide-band noises grows as a power function of duration (with an exponent of approximately .6) but not of sound pressure. For tones, binaural summation was constant but fell short of full additivity. For noises, summation changed across level and duration. Temporal summation followed the same course for monaural and binaural tonal stimuli but not for noise stimuli. Notwithstanding these differences between tone and noise, we concluded that binaural and temporal summation are independently operating integrative networks within the auditory system. The usefulness of establishing the underlying metric structure for temporal summation is emphasized.     

Dynamic frequency change influences loudness perception: a central, analytic process.

Three experiments showed that dynamic frequency change influenced loudness. Listeners heard tones that had concurrent frequency and intensity change and tracked loudness while ignoring pitch. Dynamic frequency change significantly influenced loudness. A control experiment showed that the effect depended on dynamic change and was opposite that predicted by static equal loudness contours. In a 3rd experiment, listeners heard white noise intensity change in one ear and harmonic frequency change in the other and tracked the loudness of the noise while ignoring the harmonic tone. Findings suggest that the dynamic interaction of pitch and loudness occurs centrally in the auditory system; is an analytic process; has evolved to take advantage of naturally occurring covariation of frequency and intensity; and reflects a shortcoming of traditional static models of loudness perception in a dynamic natural setting.     

Effects of changes in the intensity of white noise on simultaneity judgements and simple reaction time

On the basis of earlier work and informal observation it was suspected that the effect of loudness on simple reaction time (RT) could not be accounted for by changes in the time it takes the subject to hear the stimulus. Two experiments are described in which an increment in the level of background random noise is presented to the subject. The effect of increment size on RT and on a simultaneity judgement are investigated using a range of increments from just above difference threshold to moderately loud and clear. The difference in the size of loudness effects in the two tasks lends some support to a model which explains the influence of loudness on RT largely in terms of latency of response initiation.     

Brighter noise: Sensory enhancement of perceived loudness by concurrent visual stimulation

Two experiments investigated the effect of concurrently presented light on the perceived loudness of a low-level burst of white noise. The results suggest two points. First, white noise presented with light tends to be rated as louder than noise presented alone. Second, the enhancement in loudness judgments is resistant to two experimental manipulations: varying the probability that light accompanies sound and shifting from a rating method to a forced choice comparison. Both manipulations were previously shown to eliminate a complementary noise-induced enhancement in ratings of brightness. Whereas noise-induced enhancement of brightness seems to reflect a late-stage decisional process, such as a response bias, the present results suggest that light-induced enhancement of loudness may reflect an early-stage sensory interaction.     

The temporal weighting of loudness: effects of the level profile

In four experiments, we studied the influence of the level profile of time-varying sounds on temporal perceptual weights for loudness. The sounds consisted of contiguous wideband noise segments on which independent random-level perturbations were imposed. Experiment 1 showed that in sounds with a flat level profile, the first segment receives the highest weight (primacy effect). If, however, a gradual increase in level (fade-in) was imposed on the first few segments, the temporal weights showed a delayed primacy effect: The first unattenuated segment received the highest weight, while the fade-in segments were virtually ignored. This pattern argues against a capture of attention to the onset as the origin of the primacy effect. Experiment 2 demonstrated that listeners adjust their temporal weights to the level profile on a trial-by-trial basis. Experiment 3 ruled out potentially inferior intensity resolution at lower levels as the cause of the delayed primacy effect. Experiment 4 showed that the weighting patterns cannot be explained by perceptual segmentation of the sounds into a variable and a stable part. The results are interpreted in terms of memory and attention processes. We demonstrate that the prediction of loudness can be improved significantly by allowing for nonuniform temporal weights.     

Lunchroom noise control using feedback and group contingent reinforcement

Reduction of noise levels in an elementary school lunchroom was examined as a function of feedback and feedback plus reinforcement using group contingency procedures. Feedback consisted of signals from a traffic light, with green indicating acceptable levels, yellow indicating levels approaching undesirable, and red indicating unacceptable levels. Other behaviors, including running, hitting, pushing, and kicking, were measured incidentally. Results indicate that feedback plus reinforcement was effective in reducing noise levels. Feedback only was also effective, but to a lesser degree. No response-response relationship was found to exist between noise level and the other behaviors.     

Does a rhythmic context have an effect on perceptual weights in auditory intensity processing?

The effects of a rhythmic context on auditory intensity processing were studied. Experiment 1 tested the hypothesis that the involuntary temporal direction of attention by a rhythmic context sequence influences the temporal weighting of loudness. Perceptual weight analysis was used to measure the attention directed to individual temporal portions of a longer stimulus by estimating the importance of individual temporal segments for global loudness judgements. A rhythmic context resulted in a sharper temporal weighting profile, but the expected rhythmic pattern of weights was not observed. In Experiment 2, the accuracy for detecting a peak in the temporal loudness profile of a level-fluctuating noise was measured for the level increment presented at expected and unexpected times. The rhythmic context again caused a more pronounced temporal weighting profile. However, the accuracy was neither significantly increased for expected target segment positions nor decreased for unexpected target segment positions, relative to the condition without a rhythmic context sequence.     

Auditory perception of relative distance of traffic sounds

This study examines the accuracy of judgements of relative distance of traffic sounds (car and lorry) compared with nonattributed sounds (white noise). Adults judged whether sounds were comparatively nearer or further away in both conditions when decibel levels were the same and when decibel levels differed. Results indicated that judgement of relative distance is generally difficult and that such judgements are not based on loudness alone, particularly for traffic sounds. More errors were made when decibel levels were the same, indicating a reluctance to rely on loudness as an indicator of distance. Also more errors were made for traffic sounds. It was suggested that nonauditory criteria may be used in interpreting sounds, possibly including past experience and visual imagery. Finally, the implications of the results for road safety are discussed.     

Auditory perception of relative distance of traffic sounds

This study examines the accuracy of judgements of relative distance of traffic sounds (car and lorry) compared with nonattributed sounds (white noise). Adults judged whether sounds were comparatively nearer or further away in both conditions when decibel levels were the same and when decibel levels differed. Results indicated that judgement of relative distance is generally difficult and that such judgements are not based on loudness alone, particularly for traffic sounds. More errors were made when decibel levels were the same, indicating a reluctance to rely on loudness as an indicator of distance. Also more errors were made for traffic sounds. It was suggested that nonauditory criteria may be used in interpreting sounds, possibly including past experience and visual imagery. Finally, the implications of the results for road safety are discussed.     

Apparent warmth as a function of thermal irradiation

The skin of the back was periodically exposed to a source of radiant heat. In Experiment 1, 20 Ss matched numbers to the apparent warmth aroused by various levels of irradiant flux (method of magnitude estimation). In Experiment 2, 15 Ss matched the loudness of a white noise to the apparent uwmth aroused by the same levels used in Experiment I (method of cross-modality matching). Both experiments showed that apparent warmth is related to absorbed irradiance by a power function whose exponent is approximately 0.7.     

Asymmetry of masking between noise and tone

A pure tone was used to mask narrow and wide bands of noise centered on the frequency of the tone. In a given experimental session, the sound-pressure level (SPL) of the tone was held constant and loudness balances were obtained between a masked and unmasked noise band of equal width. These results are compared to earlier measures of the partial masking of tone by noise. The comparison shows that noise masks a tone more effectively than the tone masks the noise. Although the effect of the tone on a critical band of noise is greater than its effect on either an octave-band noise or wide-band noise, it is considerably smaller than the effect of the noise on the tone. Decreasing the noise bandwidth still further to a subcritical width reduces the asymmetry of masking somewhat, but a difference at high intensities of about 20 dB between the masking effects of an equally intense noise and tone remains. Whether the masker is a tone or noise, masking ceases when the effective energy of the masked and masking stimuli is the same.     

Discriminability, loudness, and masking in the rat (Rattus norvegicus): a confirmation and extension

In Experiment 1, rats discriminated between two sound pressure levels (SPL) of a pure tone: standard (STD) SPLs of 84 and 74 dB and comparison (CO) SPLs 4, 14, and 24 dB below STD were tested in quiet and 60 dB noise at 4 and 12.5 kHz (24 conditions). The decibel difference between STD and CO accounted for only 43.52% of the variance in the signal detection measure of sensitivity, d', across conditions, whereas the loudness difference (LD = STD0.35 - CO0.35) accounted for 89.82% of the variance in d'. These results confirm and extend previous observations that: (a) equal decibel differences are not equally discriminable; (b) loudness for the rat increases as a power function of SPL with an exponent of 0.35: and (c) masked loudness is a linear function of loudness in quiet. In Experiment 2, the assumptions of normal distribution and equal variance implicit in the use of the d' measure were examined. Receiver operating characteristic curves that were well approximated by straight lines of unit slope in normal-normal coordinates were obtained and thereby validated the use of d' in Experiment 1.