Subliminal speech perception and auditory streaming

Current theories of consciousness assume a qualitative dissociation between conscious and unconscious processing: while subliminal stimuli only elicit a transient activity, supraliminal stimuli have long-lasting influences. Nevertheless, the existence of this qualitative distinction remains controversial, as past studies confounded awareness and stimulus strength (energy, duration). Here, we used a masked speech priming method in conjunction with a submillisecond interaural delay manipulation to contrast subliminal and supraliminal processing at constant prime, mask and target strength. This delay induced a perceptual streaming effect, with the prime popping out in the supraliminal condition. By manipulating the prime-target interval (ISI), we show a qualitatively distinct profile of priming longevity as a function of prime awareness. While subliminal priming disappeared after half a second, supraliminal priming was independent of ISI. This shows that the distinction between conscious and unconscious processing depends on high-level perceptual streaming factors rather than low-level features (energy, duration).     

Anxiety sensitivity and auditory perception of heartbeat

Anxiety sensitivity (AS) is the fear of sensations associated with autonomic arousal. AS has been associated with the development and maintenance of panic disorder. Given that panic patients often rate cardiac symptoms as the most fear-provoking feature of a panic attack, AS individuals may be especially responsive to cardiac stimuli. Consequently, we developed a signal-in-white-noise detection paradigm to examine the strategies that high and low AS individuals use to detect and discriminate normal and abnormal heartbeat sounds. Compared to low AS individuals, high AS individuals demonstrated a greater propensity to report the presence of normal, but not abnormal, heartbeat sounds. High and low AS individuals did not differ in their ability to perceive normal heartbeat sounds against a background of white noise; however, high AS individuals consistently demonstrated lower ability to discriminate abnormal heartbeats from background noise and between abnormal and normal heartbeats. AS was characterized by an elevated false alarm rate across all tasks. These results suggest that heartbeat sounds may be fear-relevant cues for AS individuals, and may affect their attention and perception in tasks involving threat signals.     

Dividing attention between auditory and visual perception

To what extent is simultaneous visual and auditory perception subject to capacity limitations and attentional control? Two experiments addressed this question by asking observers to recognize test tones and test letters under selective and divided attention. In Experiment 1, both stimuli occurred on each trial, but subjects were cued in advance to process just one or both of the stimuli. In Experiment 2, subjects processed one stimulus and then the other or processed both stimuli simultaneously. Processing time was controlled using a backward recognition masking task. A significant, but small, attention effect was found in both experiments. The present positive results weaken the interpretation that previous attentional effects were due to the particular duration judgment task that was employed. The answer to the question addressed by the experiments appears to be that the degree of capacity limitations and attentional control during visual and auditory perception is small but significant.     

Phonetic categorization in auditory word perception

To investigate the interaction in speech perception of auditory information and lexical knowledge (in particular, knowledge of which phonetic sequences are words), acoustic continua varying in voice onset time were constructed so that for each acoustic continuum, one of the two possible phonetic categorizations made a word and the other did not. For example, one continuum ranged between the word dash and the nonword tash; another used the nonword dask and the word task. In two experiments, subjects showed a significant lexical effect--that is, a tendency to make phonetic categorizations that make words. This lexical effect was greater at the phoneme boundary (where auditory information is ambiguous) than at the ends of the condinua. Hence the lexical effect must arise at a stage of processing sensitive to both lexical knowledge and auditory information.     

Age-related changes in auditory temporal perception

The discrimination of signal and silence duration was evaluated in 6-month-old infants, 5 1/2-year-old children, and adults. Listeners were tested with a conditioned-discrimination procedure in which they were presented a sequence of 18 white-noise bursts and trained to discriminate a change in duration of the middle 6 signal or silence elements. There were no differential effects on performance for changes in signal compared to silence duration. At each age, performance varied only as a function of magnitude of duration change. Infants discriminated duration changes of 20 ms or greater, children discriminated 15 ms, and adults discriminated changes as small as 10 ms. These findings are consistent with other research in revealing age-related improvements in auditory temporal perception.     

Two types of auditory sequence perception

It has been suggested recently that there are two fundamentally distinct types of auditory sequence perception in man: (1) hofistic pattern recognition (HPR), operating for component item durations from a few milliseconds up to about 200 msec; and (2) direct identification of components and their order (Direct ICO), requiring verbal encoding of names for constituent sounds and requiring item durations roughly 200 msec and above for extended sequences. The present study, using only the very first judgments from 795 untrained participants presented with recycled three-item sequences, provided data consistent with this dichotomous formulation. In addition, it appeared that separate bursts of a noise band generated on-line were treated as different components in HPR and could not be used for sequence matching; “frozen” noise bursts having identical microstructure were treated as the same component and permitted HPR. On-fine noise bursts permitted Direct ICO, with naming based on long-term spectral characteristics of noise.     

Change perception in complex auditory scenes

In four experiments, we examined the role of auditory transients and auditory short-term memory in perceiving changes in a complex auditory scene comprising multiple auditory objects. Participants were presented pairs of complex auditory scenes that were composed of a maximum of four animal calls delivered in free field; participants were instructed to decide whether the two scenes were the same or different (Experiments 1, 2, and 4). Changes to the second scene consisted of either the addition or the deletion of one animal call. Contrary to intuitive predictions based on results from the visual change blindness literature, substantial deafness to the change emerged without regard to whether the scenes were separated by 500 msec of masking white noise or by 500 msec of silence (Experiment 1). In fact, change deafness was not even modulated by having the two scenes presented contiguously (i.e., 0-msec interval) or separated by 500 msec of silence (Experiments 2 and 4). This result suggests that change-related auditory transients played little or no role in change detection in complex auditory scenes. Instead, the main determinant of auditory change perception (and auditory change deafness) appears to have been the capacity of auditory short-term memory (Experiments 3 and 4). Taken together, these findings indicate that the intuitive parallels between visual and auditory change perception should be reconsidered.     

Infant auditory perception: Tonal masking

The results of an earlier study (Olsho, 1984) indicated that 5- to 8-month-old infants were relatively better at discriminating among high-frequency pitches than low. In the present study, sensory and nonsensory explanations for that effect were evaluated by examining infants' performance in a task requiring similar sensory processing but differing in the demands placed on processes such as memory. Infants' ability to resolve frequency was tested using a tonal masking paradigm, the psychophysical tuning curve. Twenty-four infants were tested at probe frequencies ranging from 500 to 4000 Hz; a group of young adults served as a comparison. Masked and unmasked thresholds were estimated using the visually reinforced head turn procedure in conjunction with an adaptive psychophysical method. Although infants' tuning curves fell below those of adults (indicating poorer performance), the widths and slopes of the infants' curves were not different from the adults'. Moreover, the difference between age groups remained constant across probe frequencies. These findings imply that by 5 months of age, the infant's ability to resolve sound frequency is similar to the adult's.     

Infants' perception of multiple-group auditory patterns

Six- and 12-month-old infants were tested for their perception of a variety of features of multiple-group auditory patterns. Each pattern comprised nine pure tones organized as three groupings each of three elements. The features examined included: (1) features having to do with frequency composition, designated as “local” pattern features; and (2) features involving relations between pattern components, designated as “global” pattern features. Infants were tested with a Go/No-Go conditioned head-turn procedure. Twelve-month-olds readily performed all discriminations. By contrast, 6-month-olds had greater difficulty discriminating local than global pattern features and showed limitations in their ability to organize three distinct groupings of elements into a unified pattern. Results are discussed with reference to infants' perception of features of single-group patterns and the notion of developmental changes in auditory information-processing capacities.     

Phasic auditory alerting improves visual conscious perception

Attention is often conceived as a gateway to consciousness (Posner, 1994). Although endogenous spatial attention may be independent of conscious perception (CP) (Koch Tsuchiya, 2007), exogenous spatial orienting seems instead to be an important modulator of CP ( [Chica et al., 2010] and Chica, Lasaponara, et al., 2011). Here, we investigate the role of auditory alerting in CP in normal observers. We used a behavioral task in which phasic alerting tones were presented either at unpredictable or at predictable time intervals prior to the occurrence of a near-threshold visual target. We find, for the first time in neurologically intact observers, that phasic alertness increases CP, both objectively and subjectively. This result is consistent with evidence showing that phasic alerting can ameliorate the spatial bias exhibited by visual neglect patients (Robertson, Mattingley, Rorden, & Driver, 1998). The alerting network may increase the activity of fronto-parietal networks involved in top-down amplification required to bring a stimulus into consciousness (Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006).     

Feature assignment in perception of auditory figure

Because the environment often includes multiple sounds that overlap in time, listeners must segregate a sound of interest (the auditory figure) from other co-occurring sounds (the unattended auditory ground). We conducted a series of experiments to clarify the principles governing the extraction of auditory figures. We distinguish between auditory "objects" (relatively punctate events, such as a dog's bark) and auditory "streams" (sounds involving a pattern over time, such as a galloping rhythm). In Experiments 1 and 2, on each trial 2 sounds-an object (a vowel) and a stream (a series of tones)-were presented with 1 target feature that could be perceptually grouped with either source. In each block of these experiments, listeners were required to attend to 1 of the 2 sounds, and report its perceived category. Across several experimental manipulations, listeners were more likely to allocate the feature to an impoverished object if the result of the grouping was a good, identifiable object. Perception of objects was quite sensitive to feature variation (noise masking), whereas perception of streams was more robust to feature variation. In Experiment 3, the number of sound sources competing for the feature was increased to 3. This produced a shift toward relying more on spatial cues than on the potential contribution of the feature to an object's perceptual quality. The results support a distinction between auditory objects and streams, and provide new information about the way that the auditory world is parsed.     

How emotional auditory stimuli modulate time perception

Emotional and neutral sounds rated for valence and arousal were used to investigate the influence of emotions on timing in reproduction and verbal estimation tasks with durations from 2 s to 6 s. Results revealed an effect of emotion on temporal judgment, with emotional stimuli judged to be longer than neutral ones for a similar arousal level. Within scalar expectancy theory (J. Gibbon, R. Church, & W. Meck, 1984), this suggests that emotion-induced activation generates an increase in pacemaker rate, leading to a longer perceived duration. A further exploration of self-assessed emotional dimensions showed an effect of valence and arousal. Negative sounds were judged to be longer than positive ones, indicating that negative stimuli generate a greater increase of activation. High-arousing stimuli were perceived to be shorter than low-arousing ones. Consistent with attentional models of timing, this seems to reflect a decrease of attention devoted to time, leading to a shorter perceived duration. These effects, robust across the 2 tasks, are limited to short intervals and overall suggest that both activation and attentional processes modulate the timing of emotional events.     

Some differences between phonetic and auditory modes of perception

When third-formant transitions are appropriately incorporated into an acoustic syllable, they provide critical support for the phonetic percepts we call [d] and [g], but when presented in isolation they are perceived as time-varying ‘chirps’. In the present experiment, both modes of perception were made available simultaneously by presenting the third-format transitions to one ear and the remainder of the acoustic syllable to the other. On the speech side of this duplex percept, where the transitions supported the perception of stop-vowel syllables, perception was categorical and influenced by the presence of a preposed [al] or [ar]. On the nonspeech side, where the same transitions were heard as ‘chirps’, perception was continuous and free of influence from the preposed syllables. As both differences occurred under conditions in which the acoustic input was constant, we should suppose that they reflect the different properties of auditory and phonetic modes of perception.     

A software tool for auditory and speech perception experimentation

A computer program capable of supporting auditory and speech perception experimentation is described. Given a continuum of acoustic stimuli, the program (Paradigm) allows the user to present those stimuli under different, well-known psychophysical paradigms (simple identification, identification with a rating scale, 2IAX, ABX, AXB, and oddity task). For discrimination tests, both high uncertainty (roving designs) and minimal psychophysical uncertainty (fixed designs) procedures are available. All the relevant time intervals can be precisely specified, and feedback is also available. Response times can be measured as well. Furthermore, the program stores subjects’ responses and provides summaries of experimental results for both individual subjects and groups. The program runs on Microsoft Windows (3.1 or 95) on personal computers equipped with any soundboard.     

Impairment of auditory perception and language comprehension in dysphasia

Men with chronic focal brain wounds were examined for their ability to discriminate complex tones, synthesized steady-state vowels, and synthesized consonant—vowel syllables. Subjects with left hemisphere damage, but not right hemisphere damage, were impaired in their ability to respond correctly to rapidly changing acoustic stimuli, regardless of whether stimuli were verbal or nonverbal. The degree of impairment in auditory processing correlated highly with the degree of language comprehension impairment. The pattern of impairment of the group with left hemisphere damage on these perceptual tests was similar to that found in children with developmental language disorders.