Similarities of low-dimensional chaotic auditory attractor sequences to quasirandom noise.

The production of sequences of sounds of various pitch levels from the algebra of chaotic attractors' trajectories is relatively straightforward. Meyer-Kress (cited in Kaneko, 1986) suggested that such sequences would be distinguishable from random independent identically distributed sequences. In psychophysical terms, this is a pattern-discrimination or pattern-similarity perception task, but these two tasks are not exactly the same thing. Nine attractors from the algebras of Henon, Zaslavskii (1978), Kaplan and Yorke (1979), Lorenz, and Gregson, and the logistic and Baker transformations, were paired with 10 realizations of a random series. The identification of the random member in each pair, the confidence of identification, and the perceived pairwise similarity were recorded by 65 subjects without initial feedback and by 76 subjects with initial feedback on five trials only, for each of 20 such pairs. The results indicate varying degrees of discriminability; they can be expressed in an analog of the receiver-operating characteristics of the attractors. There is no evidence of any homogeneous basis for the discrimination, and subjects who perform better are apparently not using the same bases as those who perform poorly. The fractal dimensionality of attractors may furnish a basis for their recognition, or the consequent autoregressive spectra induced in finite (short) samples, but recent work suggests the latter spectra can be insensitive to low-dimensional attractor dynamics.     

Identification of temporal order within auditory sequences

Unpracticed Ss reported the order of sounds in sequences consisting of either three or four successive items repeated over and over without pause. With unrelated sounds each lasting 200 msec, correct reports of order were at chance level for oral responses and for card-ordering responses (each card bearing the name of one sound). The sequences with four unrelated items were studied in greater detail, and the threshold for identification was found to be 670 msec with oral responses and 300 msec with card-ordering responses. When two related sounds (tones) were used in four-item sequences, correct card-ordering was possible at 200 msec per item when the tones were temporally contiguous, but was not possible at this duration when the tones were separated by nonrelated sounds. Some special rules governing auditory sequence identification were suggested, and implications for theories of auditory perception discussed.     

Similarities in the rate-altering effects of white noise and cocaine.

The effects of white noise and cocaine on squirrel monkeys' fixed-interval responding were compared to determine whether the presentation of an exteroceptive stimulus could produce rate-altering effects of the type typically observed following drug administration. To investigate the relationship between control response rate and response rate in the presence of drug or noise, the monkeys were trained under a fixed-interval 300-s stimulus-shock termination schedule in order to generate a wide range of local response rates. A light illuminated the experimental chamber during the interval and, after 300 s elapsed, a lever press during a 3-s period terminated the light and precluded the occurrence of a harmless electrical stimulus that otherwise was delivered at the end of the 3-s period. Each interval was followed by a 30-s timeout during which the chamber was darkened and responses had no consequences. Following intramuscular administration of cocaine, different rates of responding characteristic of control performance converged toward a common rate and, at an appropriately high dose, response rate during the fixed interval became more uniform. When white noise was presented continuously during a given session, different response rates also converged toward a common rate and, at an appropriate intensity, response rate became more uniform. Interactions were obtained when cocaine and white noise were presented together, indicating the possibility of a common behavioral mechanism of action. The results suggest that rate-altering drug effects may be, in part, a result of the ability of drugs to produce nonspecific stimulus effects similar to those observed for exteroceptive stimuli.     

The planning and execution of short auditory sequences

Action planning, but not action execution, in speeded tasks is typically faster when responses and their effects are compatible than when they are incompatible. We tested whether response-effect compatibility (REC) affects the execution of music-like sequential actions that require temporal regularity rather than rapidity. Musicians responded to metronomic visual stimuli by producing sequences of three taps at a specific tempo on three vertically aligned keys. Each tap triggered a tone. Key-to-tone mapping was either compatible or incompatible in terms of spatial height and pitch height. The results indicated that tap timing was more accurate with compatible than with incompatible mappings, both for taps produced before (Tap 1) and after (Taps 2 and 3) the onset of auditory feedback. Thus, the observed influence of REC on action execution was not due exclusively to actual auditory feedback. The anticipation of distal action effects may be involved in planning the dynamics of temporally precise movements.     

Activation of learned action sequences by auditory feedback

The present research addressed whether auditory feedback associated with a learned action sequence can activate the action representation of that sequence. Nonpianist participants learned to perform two melodies at a piano keyboard repeatedly during a trial. The participants heard feedback either from the melody they were performing (normal feedback) or from the other learned melody (termed alternate feedback). An additional tone functioned as an instruction cue to either switch melodies or continue the current melody. Following the instruction cues, participants typically paused just before switching, and paused similarly during trials with a continue cue. Participants paused longer after a continue cue when they experienced alternate rather than normal feedback. This effect was specific to instruction cues positioned at weak metrical accents—positions at which participants were less likely to switch overall. Feedback did not influence timing on switch trials. These findings indicate that influences of auditory feedback can activate learned action sequences, leading to longer latencies associated with cue evaluation.     

Effects of signal to noise variability over repeated sessions in an auditory vigilance task

Subjects listened to a sequence of Gaussian noise pulses of 0.5-sec duration, occurring at 2.5-sec intervals. Performance was compared under two conditions: One group detected the occurrence of a 1.8-dB increment in noise pulses; a second group detected the occurrence of increments of 1.3, 1.8, or 2.3 dB. All Ss performed for three 90-min sessions on different days The usual trends were noted for hits and false alarms. TSD indices, d’ and β were also derived. For both groups, it was found that d′ increased slightly over sessions and decreased almost negligibly during sessions, and criterion indices, β generally increased slightly both within and over sessions. Performance was generally comparable under the fixed- and mixed-signal conditions.     

Effect of practice on the identification of auditory sequences

Using a variant of the up-and-down method to establish duration thresholds for correct report of the order of sound sequences, six experiments were run with a practiced crew of three Ss. All showed striking improvement with practice, but substantial individual differences were observed. Two Ss found spaced sequences harder than simple cyclic ones and single presentations hardest of all, had increased difficulty when the component frequencies were brought closer together, and were disturbed by irregular timing. These variables made no difference to the third and most sensitive S, whose threshold reached 23 msec per component. All Ss displayed poorer performance if noise, additional signals, or a distrating activity occurred between the stimulus sequence and the response.     

When acoustic sequences are not perceptual sequences: The global perception of auditory patterns

Warren, Bashford, and Gardner (1990) found that when sequences consisting of 10 40-msec steady-state vowels were presented in recycled format, minimal changes in order (interchanging the position of two adjacent phonemes) produced easily recognizable differences in verbal organization, even though the vowel durations were well below the threshold for identification of order. The present study was designed to determine if this ability to discriminate between different arrangements of components is limited to speech sounds subject to verbal organization, or if it reflects a more general auditory ability. In the first experiment. 10 40-msec sinusoidal tones were substituted for the vowels; it was found that the easy discrimination of minimal changea in order is not limited to speech sounds. A second experiment substituted 10 40-msec frozen noise segments for the vowels. The succession of noise segments formed a 400-msec frozen noise pattern that cannot be considered as a sequence of individual sounds, as can the succession of vowels or tones. Nevertheless, listeners again could discriminate between patterns differing.only in the order of two adjacent 40-msec segments. These results, together with other evidence, indicate that it is not necessary foracoustic sequences of brief items (such as phonemes and tones) to be processed asperceptual sequences (that is, as a succession of discrete identifiable sounds) for different arrangements to be discriminated. Instead, component acoustic elements form distinctive “temporal compounds,” which permit listeners to distinguish between different arrangements of portions of an acoustic pattern without the need for segmentation into an ordered series of component items. Implications for models dealing with the recognition of speech and music are discussed.     

Dynamics of perceptual grouping: Similarities in the organization of visual and auditory groups

In vision, the Gestalt principles of perceptual organization are generally well understood and remain a subject of detailed analysis. However, the possibility for a unified theory of grouping across visual and auditory modalities remains largely unexplored. Here we present examples of auditory and visual Gestalt grouping, which share important organizational properties. In particular, similarities are revealed between grouping processes in apparent motion, auditory streaming, and static 2-D displays. Given the substantial difference in the context, within which the phenomena in question occur (auditory vs. visual, static vs. dynamic), these similarities suggest that the dynamics of perceptual organization could be associated with a common (possibly central) mechanism. If the relevance of supramodal invariants of grouping is granted, the question arises as to whether they can be studied empirically. We propose that a “force-field” theory, based on a differential-geometric interpretation of perceptual space, could provide a suitable starting point for a systematic exploration of the subjective properties of certain classes of auditory and visual grouping phenomena.     

Lateralization of an auditory signal in correlated noise and in uncorrelated noise as a function of signal frequency

Listeners lateralized a monaural signal presented against a continuous background of perfectly correlated noise (NO) or of uncorrelated noise (NU). Measures of signal detectability were also secured in separate tests. Psychometric functions (percent correct vs signal energy) were determined for each task. For a tonal signal of either low or high frequency, a listener requires only slightly greater signal energy (about 1 dB) in order to lateralize as well as he can detect when the noise is uncorrelated (NU). When the noise is perfectly correlated (NO), the slope of the psychometric function for lateralization depends upon signal frequency. With 250 Hz, the slope of the psychometric function for lateralization is much smaller than that for detection. With 1,000 Hz, the function for lateralization is steeper than that for 250 Hz, but the slope is still less than that of the function for detection for 1,000 Hz. With 2,000 Hz, the function for lateralization has about the same slope as that for detection.     

Body movement enhances the extraction of temporal structures in auditory sequences

Auditory and motor systems interact in processing auditory rhythms. This study investigated the effect of intuitive body movement, such as head nodding or foot tapping, on listeners’ ability to entrain to the pulse of an auditory sequence. A pulse-finding task was employed using an isochronous sequence of tones in which tones were omitted at pseudorandom positions. Musicians and non-musicians identified their subjectively fitting pulse either using periodic body movement or through listening only. The identified pulse was measured subsequently by finger tapping. Movement appeared to assist pulse extraction especially for non-musicians. The chosen pulse tempi tended to be faster with movement. Additionally, movement led to higher synchronization stabilities of the produced pulse along the sequence, regardless of musical training. These findings demonstrated the facilitatory role of body movement in entraining to auditory rhythms and its interaction with musical training.     

Working memory for patterned sequences of auditory objects in a songbird

The capacity to remember sequences is critical to many behaviors, such as navigation and communication. Adult humans readily recall the serial order of auditory items, and this ability is commonly understood to support, in part, the speech processing for language comprehension. Theories of short-term serial recall posit either use of absolute (hierarchically structured) or relative (associatively structured) position information. To date, neither of these classes of theories has been tested in a comparative auditory model. European starlings, a species of songbird, use temporally structured acoustic signals to communicate, and thus have the potential to serve as a model system for auditory working memory. Here, we explore the strategies that starlings use to detect the serial order of ecologically valid acoustic communication signals and the limits on their capacities to do so. Using a two-alternative choice operant procedure, we demonstrate that starlings can attend to the serial ordering of at least four song elements (motifs) and can use this information to classify differently ordered sequences of motifs. Removing absolute position cues from sequences while leaving relative position cues intact, causes recognition to fail. We then show that starlings can, however, recognize motif-sequences using only relative position cues, but only under rigid circumstances. The data are consistent with a strong learning bias against relative position information, and suggest that recognition of structured vocal signals in this species is inherently hierarchical.     

Modality-constrained statistical learning of tactile, visual, and auditory sequences

The authors investigated the extent to which touch, vision, and audition mediate the processing of statistical regularities within sequential input. Few researchers have conducted rigorous comparisons across sensory modalities; in particular, the sense of touch has been virtually ignored. The current data reveal not only commonalities but also modality constraints affecting statistical learning across the senses. To be specific, the authors found that the auditory modality displayed a quantitative learning advantage compared with vision and touch. In addition, they discovered qualitative learning biases among the senses: Primarily, audition afforded better learning for the final part of input sequences. These findings are discussed in terms of whether statistical learning is likely to consist of a single, unitary mechanism or multiple, modality-constrained ones.     

Infants' perception of rhythm: categorization of auditory sequences by temporal structure

We presented 7- to 9-month-old infants with repetitions of three- or four-tone sequences characterized by a particular rhythmic structure. We then evaluated their detection of changes in rhythmic structure in the context of randomly presented variations in tempo (rate) and frequency. Infants successfully differentiated between three-tones sequences with 1, 2 (X XX) and 2, 1 (XX X) structure as well as four-tone sequences with 2, 2 (XX XX) and 3, 1 (XXX X) structure. In other tasks, they indicated their ability to discriminate between contrasting tempos in the context of frequency variations. We conclude, then, that infants can categorize auditory sequences on the basis of rhythm and also on the basis of tempo.     

Hearing what the eyes see: auditory encoding of visual temporal sequences

When the senses deliver conflicting information, vision dominates spatial processing, and audition dominates temporal processing. We asked whether this sensory specialization results in cross-modal encoding of unisensory input into the task-appropriate modality. Specifically, we investigated whether visually portrayed temporal structure receives automatic, obligatory encoding in the auditory domain. In three experiments, observers judged whether the changes in two successive visual sequences followed the same or different rhythms. We assessed temporal representations by measuring the extent to which both task-irrelevant auditory information and task-irrelevant visual information interfered with rhythm discrimination. Incongruent auditory information significantly disrupted task performance, particularly when presented during encoding; by contrast, varying the nature of the rhythm-depicting visual changes had minimal impact on performance. Evidently, the perceptual system automatically and obligatorily abstracts temporal structure from its visual form and represents this structure using an auditory code, resulting in the experience of "hearing visual rhythms."     

Effects of auditory masking by white noise on primary stressing during spontaneous speech

6 adult subjects (3 men, 3 women) produced highly similar spontaneous speech utterances in quiet and with 90-dB SPL white noise. The frequency of occurrence of perceptual judgments of primary stressing in an utterance was not affected by the masking noise. This finding supplements our previous report that variability for stress production of fundamental frequency (fo) during spontaneous speech was preserved under short-term auditory disruption. Also, it adds further support to the contention that fo is under open-loop regulation.     

Picking up the pace: effects of global temporal context on sensitivity to the tempo of auditory sequences

This article continues a line of research examining factors affecting listeners' auditory tempo sensitivities. Of particular interest is the question of whether listeners are sensitive to the overall (global) pace of their auditory environment and how this sensitivity may affect their perceptions of sequence timing. To address this question, we manipulated the set of sequence tempi (between 300 and 700 msec) that listeners experienced over the course of a 1-h period (i.e., the global temporal context) while they performed a tempo-discrimination task involving standard-comparison pairs of isochronous tone sequences. Overall findings show systematic distortions in perceived tempo that are consistent with the view that listeners adapt to the global pace of their auditory environments. Moreover, general support was found for the hypothesis that increasing the number of equal intervals in a standard sequence produces greater improvements in tempo sensitivity when the standard sequence tempo is different from the global pace than when it is at the global pace. Implications of these findings for models of timing and temporal processing are discussed.     

On the nature of phase attraction in sensorimotor synchronization with interleaved auditory sequences

In a task that requires in-phase synchronization of finger taps with an isochronous sequence of target tones that is interleaved with a sequence of distractor tones at various fixed phase relationships, the taps tend to be attracted to the distractor tones, especially when the distractor tones closely precede the target tones [Repp, B. H. (2003a). Phase attraction in sensorimotor synchronization with auditory sequences: Effects of single and periodic distractors on synchronization accuracy. Journal of Experimental Psychology: Human Perception and Performance, 29, 290-309]. The present research addressed two related questions about this distractor effect: (1) Is it a function of the absolute temporal separation or of the relative phase of the two stimulus sequences? (2) Is it the result of perceptual grouping (integration) of target and distractor tones or of simultaneous attraction to two independent sequences? In three experiments, distractor effects were compared across two different sequence rates. The results suggest that absolute temporal separation, not relative phase, is the critical variable. Experiment 3 also included an anti-phase tapping task that addressed the second question directly. The results suggest that the attraction of taps to distractor tones is caused mainly by temporal integration of target and distractor tones within a fixed window of 100-150 ms duration, with the earlier-occurring tone being weighted more strongly than the later-occurring one.