Auditory temporal discrimination by trained listeners

Previous reports from this laboratory have shown that untrained listeners cannot name the order of sounds in extended sequences of unrelated items such as hisses, tones, and buzzes at item durations of 200 msec, even though identification of order for the sounds of speech and music is accomplished readily at much shorter item durations. The present study indicates that under appropriate conditions subjects can be trained to distinguish between and to identify permuted orders within sequences of nonrelated sounds each lasting only 10 msec or less. Evidence is presented suggesting that much of what passes for direct identification of order is actually based on prior identification of a larger pattern. Two principal mechanisms seem to mediate discrimination of auditory temporal order: (1) fine resolution (requiring prior training) permitting identification of over-all patterns and capable of operating with item durations of only a few msec; (2) coarse resolution (special prior training not required) allowing naming of order of items having minimal durations usually above 200 msec for unfamiliar sequences.     

Auditory frequency discrimination in adult developmental dyslexics

Developmental dyslexics reportedly discriminate auditory frequency poorly. A recent study found no such deficit. Unlike its predecessors, however, it employed multiple exposures per trial to the standard stimulus. To investigate whether this affects frequency discrimination in dyslexics, a traditional two-interval same-different paradigm (2I_1A_X) and a variant with six A-stimuli per trial (2I_6A_X) were used here. Frequency varied around 500 Hz; interstimulus interval (ISI) ranged between 0 and 1,000 msec. Under 2I_1A_X, dyslexics always had larger just noticeable differences (JNDs) than did controls. Dyslexic and control JNDs were equal at shorter ISIs under 2I_6A_X, but dyslexics became worse than controls at longer ISIs. Signal detection analysis suggests that both sensory variance and trace variance are larger in dyslexics than in controls.     

Auditory evoked potential correlates of speech sound discrimination

An electrophysiological correlate of the discrimination of stop consonants drawn from within and across phonetic categories was investigated by an auditory evoked response (AER) technique. Ss were presented a string of stimuli from the phonetic category [ba] (the standard stimulus) and were asked to detect the occurrence of a stimulus from the same phonetic category (within-category shift), or the occurrence of a stimulus from a different phonetic category [pa] (across-category shift). Both the across- and within-category shift stimuli differed equally from the standard stimulus in the time of onset of the first formant and in the amount of aspiration in the second and third formants. The NIP2 response of the AER was larger to the across-category shift than to the within-category shift. The within-category shift did not differ from a no-shift control. These findings suggest (1) that the AER can reflect the relative discriminability of stop consonants drawn from the same or different phonetic categories in a manner similar to other behavioral measures; (2) that the detailed acoustic representation of stop consonants is transformed into a categorized phonetic representation within 200 msec after stimulus onset.     

Auditory discrimination: a three-variable analysis of intensity effects

The acquisition of auditory intensity discriminations in rats trained on multiple variable-interval extinction schedules was studied as a function of some of the variables that contribute to the speed of development of differential responding and the final level attained. The effects of three variables were isolated and studied in detail: (1) the decibel difference between the discriminative stimuli (intensity difference); (2) the intensity relationship between the stimuli (relative intensity); and (3) the position of the stimuli on the intensity continuum (absolute intensity). Each of the three variables generated orderly relationships and interacted with one another to produce complex effects upon differential responding.     

Auditory frequency discrimination learning is affected by stimulus variability

We explored the effects of training set variability on learning and generalization of pure-tone frequency discrimination (FD) in three groups of untrained, normally hearing adult listeners. Group 1 trained using a fixed standard tone at 1 kHz (fixed), Group 2 on slightly varying (roving) tones around 1 kHz, and Group 3 on widely varying standard frequencies (wide-roving). Initially, two thirds of all listeners had low FD thresholds (good listeners) and one third had intermediate to high thresholds (poor listeners). For good listeners, slight variations in the training set slowed learning but wide variations did not. Transfer to untrained frequencies (up to 4 kHz) and to the fixed condition was equivalent regardless of training condition, but Group 1 listeners did not fully transfer learning to the roving condition. For poor listeners, any variation in the training condition slowed learning and impaired transfer to other frequencies but did not affect transfer to untrained conditions. Thus, the effects of training set on progress and outcome depend on set variability and individual FD ability.     

Crossmodal attention switching: Auditory dominance in temporal discrimination tasks

Visual stimuli are often processed more efficiently than accompanying stimuli in another modality. In line with this “visual dominance”, earlier studies on attentional switching showed a clear benefit for visual stimuli in a bimodal visual–auditory modality-switch paradigm that required spatial stimulus localization in the relevant modality. The present study aimed to examine the generality of this visual dominance effect. The modality appropriateness hypothesis proposes that stimuli in different modalities are differentially effectively processed depending on the task dimension, so that processing of visual stimuli is favored in the dimension of space, whereas processing auditory stimuli is favored in the dimension of time. In the present study, we examined this proposition by using a temporal duration judgment in a bimodal visual–auditory switching paradigm. Two experiments demonstrated that crossmodal interference (i.e., temporal stimulus congruence) was larger for visual stimuli than for auditory stimuli, suggesting auditory dominance when performing temporal judgment tasks. However, attention switch costs were larger for the auditory modality than for visual modality, indicating a dissociation of the mechanisms underlying crossmodal competition in stimulus processing and modality-specific biasing of attentional set.     

Auditory phase and frequency discrimination: a comparison of nine procedures

Two auditory discrimination tasks were thoroughly investigated: discrimination of frequency differences from a sinusoidal signal of 200 Hz and discrimination of differences in relative phase of mixed sinusoids of 200 Hz and 400 Hz. For each task psychometric functions were constructed for three observers, using nine different psychophysical measurement procedures. These procedures included yes-no, two-interval forced-choice, and various fixed- and variable-standard designs that investigators have used in recent years. The data showed wide ranges of apparent sensitivity. For frequency discrimination, models derived from signal detection theory for each psychophysical procedure seem to account for the performance differences. For phase discrimination the models do not account for the data. We conclude that for some discriminative continua the assumptions of signal detection theory are appropriate, and underlying sensitivity may be derived from raw data by appropriate transformations. For other continua the models of signal detection theory are probably inappropriate; we speculate that phase might be discriminable only on the basis of comparison or change and suggest some tests of our hypothesis.     

Auditory discrimination learning: Prototype storage and distinctive features detection mechanisms

The relative contributions of prototype storage and distinctive features detection mechanisms hypothesized to be operating in successive discrimination learning were assessed by the extent of negative transfer between auditory discrimination tasks. The results indicated that both mechanisms were involved, but that prototype storage was the dominant process. This outcome is compared with previous research on tactual and visual discrimination learning. Experimental variables are suggested that might control which mechanism predominates.     

Auditory and phonetic memory codes in the discrimination of consonants and vowels

Recognition memory for consonants and vowels selected from within and between phonetic categories was examined in a delayed comparison discrimination task. Accuracy of discrimination for synthetic vowels selected from both within and between categories was inversely related to the magnitude of the comparison interval. In contrast, discrimination of synthetic stop consonants remained relatively stable both within and between categories. The results indicate that differences in discrimination between consonants and vowels are primarily due to the differential availability of auditory short-term memory for the acoustic cues distinguishing these two classes of speech sounds. The findings provide evidence for distinct auditory and phonetic memory codes in speech perception.     

Oculomotor consequences of abrupt object onsets and offsets: onsets dominate oculomotor capture

Previous research has shown that the appearance of an object (onset) and the disappearance of an object (offset) have the ability to influence the allocation of covert attention. To determine whether both onsets and offsets have the ability to influence eye movements, a series of experiments was conducted in which participants had to make goal-directed eye movements to a color singleton target in the presence of an irrelevant onset/offset. In accord with previous research, onsets had the ability to capture the eyes. The offset of an object demonstrated little or no ability to interrupt goal-directed eye movements to the target. Two experiments in which the effects of onsets and offsets on covert attention were examined suggest that offsets do not capture the eyes, because they have a lesser ability to capture covert attention than do onsets. A number of other studies that have shown strong effects of offsets on attention have used offsets that were uncorrelated with target position (i.e., nonpredictive), whereas we used onsets and offsets that never served as targets (i.e., antipredictive). The present results are consistent with a new-object theory of attentional capture in which onsets receive attentional priority over other types of changes in the visual environment.     

Attention capture by contour onsets and offsets: No special role for onsets

In five experiments, we investigated the power of targets defined by the onset or offset of one of an object’s parts (contour onsets and offsets) either to guide or to capture visual attention. In Experiment 1, search for a single contour onset target was compared with search for a single contour offset target against a static background of distractors; no difference was found between the efficiency with which each could be detected. In Experiment 2, onsets and offsets were compared for automatic attention capture, when both occurred simultaneously. Unlike in previous studies, the effects of overall luminance change, new-object creation, and number of onset and offset items were controlled. It was found that contour onset and offset items captured attention equally well. However, display size effects on both target types were also apparent. Such effects may have been due to competition for selection between multiple onset and offset stimuli. In Experiments 3 and 4, single onset and offset stimuli were presented simultaneously and pitted directly against one another among a background of static distractors. In Experiment 3, we examined “guided search,” for a target that was formed either from an onset or from an offset among static items. In Experiment 4, the onsets and offsets were uncorrelated with the target location. Similar results occurred in both experiments: target onsets and offsets were detected more efficiently than static stimuli which needed serial search; there remained effects of display size on performance; but there was still no advantage for onsets. In Experiment 5, we examined automatic attention capture by single onset and offset stimuli presented individually among static distractors. Again, there was no advantage for onset over offset targets and a display size effect was also present. These results suggest that, both in isolation and in competition, onsets that do not form new objects neither guide nor gain automatic attention more efficiently than offsets. In addition, in contrast to previous studies in which onsets formed new objects, contour onsets and offsets did not reliably capture attention automatically.     

Auditory discrimination, intelligence, and reading achievement at grade 1.

To determine the relations of auditory discrimination and intelligence to reading achievement in first grade the California Test of Mental Maturity, the California Achievement Test (reading), and the Buktenica Modification of the Wepman Auditory Discrimination Test were administered to 78 first grade students. Correlations suggested a stronger relation between auditory discrimination and reading than between IQ and reading as measured here; however, range of reading scores were restricted. Results support Wepman's developmental theory. The methodological approach includes simultaneous consideration of effects of auditory discrimination and intelligence.     

Abrupt onsets cannot be ignored

Participants identified target letters at cued locations in the presence of occasional abrupt onsets of new distractor letters. The onsets distracted the participants and impaired their letter identification performance despite confirmation that they were using the information provided by the cue. This result contrasts with earlier results found by other researchers that revealed an ability of participants to ignore abrupt onsets in some cases. Our results, however, were obtained under conditions that prevented anticipatory eye movements to the target. In a subsequent experiment when participants were permitted to look at the target in advance, the distracting effect of the onsets was eliminated, suggesting that participants may have looked at the target in the earlier studies. We conclude that abrupt onsets cannot be ignored unless the target element receives a substantial advantage via fixation.     

Auditory discrimination: role of time and intensity in the precedence effect.

Rats were trained to respond on a lever adjacent to a sounding speaker (the sound source) when a single click was emitted. A second click (the artificial echo) was presented through a second speaker on the opposite side. In Condition I, the echo (equal in intensity to the source) was delayed from .015 to 32 milliseconds; greater than 75% correct responses were given for delay times between about .040 milliseconds (lower threshold) and 8 milliseconds (upper threshold). In Condition II, the echo (simultaneous with the source) was reduced in intensity relative to the source over a range from 2.5 decibels to 40 decibels; greater than 75% correct responses occurred for intensity reductions greater than 5 decibels. In Condition III, both the intensity and the delay time of the echo were manipulated in a manner analogous to that which would occur under natural conditions; greater than 95% correct responses were given for delay times from 1 to 32 milliseconds. These data indicate that both time and intensity differences are necessary for localization of primary sources, with delay time contributing more at short echo path distances, and intensity differences at long distances.     

Auditory phonemic perception in dyslexia: Categorical identification and discrimination of stop consonants

The possibility that phonological confusions may underlie some difficulties in processing written language was investigated using four speech perception tasks. Twelve dyslexic and four normal-reading children identified and discriminated synthetic speech syllables which varied either in voice-onset time (signaling the feature of voicing) or direction of formant transitions (signaling place of articulation). Results indicate that, like normal-reading children and adults, dyslexic children perceive these sounds categorically. Discrimination of the stimuli was limited by their identifiability. It is suggested that linguistic disturbances at other stages of the grapheme to meaning transformation underlie misreading.     

Auditory discrimination of anisochrony: influence of the tempo and musical backgrounds of listeners

This study explored the influence of several factors, physical and human, on anisochrony's thresholds measured with an adaptive two alternative forced choice paradigm. The effect of the number and duration of sounds on anisochrony discrimination was tested in the first experiment as well as potential interactions between each of these factors and tempo. In the second experiment, the tempo or the inter onset interval (IOI) was varied systematically between 80 and 1000 ms. The results showed that just noticeable differences increase linearly and proportionally with IOI in accordance with Weber's law except for quickest tempo (IOI of 80 ms). The third experiment investigated the role of musical training on anisochrony thresholds obtained for different IOI. It focused on differential effects of musical experiences by comparing non-musicians, instrumentalists, and percussionists thresholds. The results of the present study replicated the findings of previous experiments regarding the adequacy of Weber's law for slow rhythm and provided evidence for its departure for fast tempos. Moreover, thresholds from percussionists seem distinguishable from the ones of other listeners by their highest sensitivity to temporal shifts suggesting therefore the necessity to control the nature of musical experiences. The results are discussed according to current models of time perception.     

Auditory pattern perception: The effect of tone location on the discrimination of tonal sequences

This study examined the effect of tonal location on the discrimination of sequences differing in the order of the tones and on their perceived grouping. The frequency range between the sequential tones was held constant. When all tones came from the same location, the sequence was rated as integrated, but when the higher frequency tones came from a different location than the lower frequency tones, the sequence was rated as segregated. Listeners discriminated the sequences in a 3EFC task. Discrimination performance was impaired when the sequence was split between two locations and tonal order was changed in only one location, even though the order of tones in different locations was changed. This result suggests that listeners have difficulty relating tones across locations or in different perceptual groups. Performance in this experiment is generally better than that observed by Barsz (1988), and it is suggested that the level of stimulus uncertainty explains this difference.     

Syllable onsets are perceptual reading units

Syllable onsets are defined as the initial consonant or consonant cluster in a syllable (e.g., BR in BREAD). In the present study, using a letter detection paradigm and French words, we tested whether syllable onsets are processed as units by the reading system. In Experiment 1, we replicated Gross, Treiman, and Inman's (2000) result of observing no difference between the detection latencies of letters embedded in a multi-letter syllable onset (e.g., c in ECLATER) relative to a single-letter syllable onset (e.g., C in ECARTER). In Experiment 2, participants took longer to detect the target letter when it was in the second position of a multi-letter onset (e.g., L in TABLIER) than when it was a single-letter onset (e.g., L in ECOLIER). In Experiment 3, this position effect was replicated for graphemes. In Experiment 4, we tested and ruled out an alternative explanation of the unitization effect, in terms of lateral masking. These results indicate that syllable onsets are processed as perceptual units by the reading system and that the unitization effect is position dependent.