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PubMed1982

Measures of intensity discrimination.

Several different measures have been employed in the literature to describe performance by human observers in intensity discrimination tasks. These measures include the difference limen (DL) or "delta I in dB," the Weber fraction (delta I/I), and signal-to-masker ratio (Ps/Pm). This article describes the mathematical relationship among these measures for conditions in which masker and signal are (1) sinusoids of the same frequency; (2) sinusoids of different frequencies; and (3) noise waveforms. We provide a table which contains values of each of these measures, describing equivalent performance over the typical range obtained in most intensity discrimination experiments. We express some cautions that should be observed in choosing and reporting particular measures of intensity discrimination.

Humans↗
PubMed1987

Temporal factors in the discrimination of tonal sequences.

Human observers were asked to judge whether or not two sequences of eight or more tones had the same serial pattern of frequencies. The temporal envelopes of the sequences were manipulated by randomly varying the tone durations or intertone gaps. In the correlated condition, the temporal envelopes of the sequences were varied across trials; the two sequences within each trial had the same temporal envelope. In the uncorrelated condition, the temporal envelopes were varied both across and within trials; every sequence had a unique temporal pattern. Performance in the uncorrelated condition decreased with increased variability in the temporal envelope. Performance in the correlated condition was independent of temporal variability, but decreased with increases in the time interval between the onsets of the two sequences. This pattern of results is consistent with an extension of a model of auditory discrimination developed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372-383 (1969)], in which two processing modes are postulated: a trace mode and a context mode. When the tonal sequences had unique temporal patterns, context mode processing was dominant; when the sequences had identical temporal patterns, trace mode processing was preferred. The effect of variables such as the number of tones, the tone duration, the time gap between tones, and the time interval between sequences was consistent with the predictions of the discrimination model.

Attention↗
PubMed2005

Optimizing the clinical fit of auditory brain stem implants.

OBJECTIVE: To develop and implement a new audiological fitting procedure for auditory brain stem implants (ABIs), based on an efficient algorithm, and to compare it with two procedures presently used in clinical practice. DESIGN: First, the different procedures were compared by using computer models and simulations with normal-hearing subjects (N = 4). This allows for an analysis of the accuracy of the procedures in a way that is not possible when testing ABI users. The root-mean-square error between the order estimated by the procedure and the true order was calculated. In addition, ABI users (N = 2) were tested with the new procedure to see if it could be successfully applied in clinic. The degree of variability of their results across runs and sessions was analyzed. RESULTS: The tests of the normal-hearing subjects showed that our proposed procedure required significantly fewer trials (22 on average) than procedures presently used in clinic (with 76 and 234 trials on average for the two other procedures tested) to produce the same degree of accuracy. Computer modeling also demonstrated this advantage. Additional testing showed this advantage was maintained under a variety of conditions relevant to the clinic. The two patients tested were able to use this procedure with success, even though they were poor at discriminating the pitch of electrodes. The patients showed results consistent with having about 4 to 5 discriminable groups of electrodes with the 12 to 14 electrodes tested. CONCLUSIONS: The proposed procedure requires fewer trials to produce a clinically useful result and is well tolerated in the clinic. An additional advantage is that it allows testing to be broken down into several "blocks," each containing a small number of trials. If the variability between blocks is small, information can be combined across blocks to increase the accuracy of the result. If the variability is large, perhaps between blocks on different days, this may reflect a significant change in the percepts generated by the implant, and signal to the clinician that a significant alteration in the fitting is required. We recommend its use in ABI user fitting and in cochlear implant fitting when pitch ranking is problematic.

Adult↗
PubMed1994

Robustness of individual identity in the cries of human infants.

This study investigated the possibility that one function of the human infant's cry is to convey individual identity across distance. Six-hundred adults, having been exposed to 30 s of an infant's crying, were asked to identify this infant on the basis of other, experimentally altered, cries. The cries were altered naturally by rerecording across distance in the out-of-doors, and artificially by bandpass filtering and temporal reorganization. The individuality of cries proved remarkably robust to degradation: Only when frequencies were limited to the range of 8 to 10 kHz was recognition performance significantly impaired. It is argued that the human infant's cry, a complex signal with multiple markers of individuality, may have among its functions the communication of infants' identities across distance.

Adolescent↗
PubMed1975

Effects of time and tasks upon auditory and somatosensory evoked potentials in man.

Auditory evoked potentials (AEPs) recorded from the vertex and somatosensory evoked potentials (SEPs) recorded from the somatosensory and motor areas and vertex were examined during visual and auditory discrimination tasks, with and without motor responses, and during motor tasks alone in normal human subjects. These procedures allowed the separation of sensory discrimination from motor activity effects on the evoked potentials. It was observed that EPs were modified systematically by task and by temporal variables, even though vigilance, as evaluated through EEG recording and performance level, was stable throughout the experimental recording session. 1. AEPs were minimally influenced by time, but very sensitive to task. Inversely, the SEP amplitude decreased considerably with time and less with task. There was evidence of time/task interaction. 2. The magnitude of SEP attenuation in time was reduced by intervening rest periods. 3. The sensory modality in which the discrimination task was performed did not influence the effect on EPs. A discrimination task involving a motor response reduced EPs more than a pure discrimination or a pure motor task. The task effect seems to involve a general, mechanism (load imposed upon the subject) not dependent on the particular sensory channel used to deliver task-relevant information.

Auditory Cortex↗
PubMed1982

Avian and primate communication: the problem of natural categories.

To negotiate effectively with the world on the basis of experience, organisms must classify past events with rules about when to lump stimulus variants into perceptual categories and when to treat them separately. In nature, tactics for evading capture vary with the predator. Appropriately, adult monkey alarm calls are specifically linked to predator category. Linkages are less precise in one-month infants but they discriminate between major predator categories. Associations become more highly specified with experience. Birds discriminate innately between conspecific and alien songs, but vocal perception is subsequently enriched by experience. Monkeys also use special processing in categorizing their own vocal repertoire. In forming perceptual categories birds and monkeys evidently use species-specific predispositions that focus attention on biologically relevant stimuli and ensure commonality in rules used by species members in perceptual analysis. Thus animals are led to share natural perceptual categories to which meaningful communicative labels can be attached.

Animal Communication↗
PubMed2004

Pulse rate discrimination with deeply inserted electrode arrays.

Pulse rate difference limen (PRDL) and amplitude modulation difference limen (AMDL) were assessed as a function of base rate and cochlear electrode location in seven (three for AMDL) subjects implanted with the MED-EL COMBI 40+ implant. The MED-EL COMBI 40+ electrode array allows deep insertion of the electrode up to the apex of the cochlea to minimize the rate/place mismatch for pulse rates below 500 pps. A three interval, two alternative forced-choice procedure with feedback was used to measure the difference limen. The base rate was in the range between 200 and 800 pps. The carrier rate for the AMDL measurement was 5081 pps. The PRDL increased with increasing base pulse rate. At 200 pps the average PRDL measured at the apical electrode amounted to 48.7 pps, at 400 pps the average PRDL reached 206.6 pps. No significant difference between PRDL obtained from apical or basal electrodes could be observed. AMDL was higher than PRDL at all tested base rates. The ability to discriminate rate changes is limited to base rates up to about 283 pps. The results indicate that rate changes smaller than a major third do not elicit distinguishable auditory perceptions in electrical hearing. The absence of a difference between apical and basal electrode locations indicates that a reduction of the rate/place mismatch does not improve discrimination performance.

Adult↗
PubMed1993

Common factors in the identification of an assortment of brief everyday sounds.

Acoustic, ecological, perceptual and cognitive factors that are common in the identification of 41 brief, varied sounds were evaluated. In Experiment 1, identification time and accuracy, causal uncertainty values, and spectral and temporal properties of the sounds were obtained. Experiment 2 was a survey to obtain ecological frequency counts. Experiment 3 solicited perceptual-cognitive ratings. Factor analyses of spectral parameters and perceptual-cognitive ratings were performed. Identification time and causal uncertainty are highly interrelated, and both are related to ecological frequency and the presence of harmonics and similar spectral bursts. Experiments 4 and 5 used a priming paradigm to verify correlational relationships between identification time and causal uncertainty and to assess the effect of sound typicality. Results support a hybrid approach for theories of everyday sound identification.

Adult↗
PubMed1978

Critical-band effects in two-channel auditory signal detection.

Two-channel auditory signal detection was investigated with 50-msec sinusoidal signals masked by binaurally uncorrelated noise. In the two-channel tasks, the signals in each earphone channel were presented with an independent probability during the single observation interval and the observers were required to detect the inputs in a single earphone (selective-attention condition) or in both earphones (divided-attention condition). When the signals in each earphone were within the same critical band (the assumed singled processing unit in frequency domain), there was a decrement in detection performance in both the selective- and divided-attention (i.e. dichotic) conditions compared with the monaural condition. However, when signals were separated in frequency by several critical bands, a decrement in dichotic performance, as compared with monaural performance, occurred only in the divided-attention condition. These findings are discussed in terms of their implications regarding models of multichannel signal processing and the definition of input channels in terms of earphones.

Attention↗
PubMed1978

Levels of processing in speech perception.

Four experiments are reported investigating previous findings that speech perception interferes with concurrent verbal memory but difficult nonverbal perceptual tasks do not, to any great degree. The forgetting produced by processing noisy speech could not be attributed to task difficulty, since equally difficult nonspeech tasks did not produce forgetting, and the extent of forgetting produced by speech could be manipulated independently of task difficulty. The forgetting could not be attributed to similarity between memory material and speech stimuli, since clear speech, analyzed in a simple and probably acoustically mediated discrimination task, produced little forgetting. The forgetting could not be attributed to a combination of similarity and difficutly since a very easy speech task involving clear speech produced as much forgetting as noisy speech tasks, as long as overt reproduction of the stimuli was required. By assuming that noisy speech and overtly reproduced speech are processed at a phonetic level but that clear, repetitive speech can be processed at a purely acoustic level, the forgetting produced by speech perception could be entirely attributed to the level at which the speech was processed. In a final experiment, results were obtained which suggest that if prior set induces processing of noisy and clear speech at comparable levels, the difference between the effects of noisy speech processing and clear speech processing on concurrent memory is completely eliminated.

Acoustics↗
PubMed1979

Similarity effects in backward recognition masking.

Auditory backward recognition masking refers to the ability of a masking sound to terminate further perceptual resolution of a test sound presented slightly earlier in time. The present experiments were conducted to determine whether mask/test tone similarity effects in backward recognition masking could be reliably demonstrated. Although similarity effects were found in Experiments 1 and 2, only about 60% of the subjects demonstrated these effects. Experiment 3 was designed to isolate which stage of information processing is responsible for similarity effects. It was hypothesized that similarity effects are due to mask interference with the synthesized auditory memory of the test tone rather than to selective overwriting of a preperceptual auditory store: previous research has shown that interference in synthesized auditory memory depends on the similarity of the interfering stimulus to the items held in memory. By independently varying the backward masking interval and the interfering effect of the mask on the test tone memory, it was possible to demonstrate that similarity effects are indeed caused by mask interference in synthesized memory. The implications of these results are considered in the framework of auditory and visual masking.

Auditory Perception↗
PubMed1990

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): II. Synthetic calls.

In 2 experiments classification of synthetic versions of species-typical snake and eagle alarm calls by vervet monkeys (Cercopithecus aethiops) and human (Homo sapiens) control subjects was investigated. In a 2-choice, operant-conditioning-based procedure, this work followed up acoustic analyses that had used various digitally based algorithms (Owren & Bernacki, 1988). All subjects were first tested with alarm-call replicas that were based on analysis data. These models were classified in the same manner as natural stimuli, which verified the appropriateness of the acoustic characterizations. Synthetic stimuli were then presented to test the importance of specific acoustic cues. Spectral patterning was found to be the most salient cue for classification by the monkeys, whereas results from the human subjects were mixed. Implications for the study of nonhuman primate vocalizations and Lieberman's (1984) theory of speech evolution are discussed.

Adult↗
PubMed1984

The functional analysis of auditory discrimination.

Mammals have evolved the ability to acquire auditory discriminations. The characteristics of this discriminative ability presumably fit the natural conditions under which discriminations are normally acquired. The purpose of this paper is to review experiments which were directed at showing that auditory discriminations are most rapidly acquired when natural features are incorporated into the experiments. The experiments were also directed at discovering the underlying characteristics of the discriminative ability. When animals were trained to discriminate the position of a sound source in which natural features were incorporated into the experiment, the discrimination was acquired in one trial. Manipulation of the natural features suggested that one trial acquisition depends upon the following. (1) Stimulus novelty; the effect of reinforcement is stronger in the presence of novel than familiar stimuli. (2) Specific behavioral effect of reinforcement; the effect of reinforcing a response in the presence of a novel auditory stimulus is to increase the strength of approaching and manipulating the sound source.

Animals↗