A precedence effect in the processing of verbal information.

When a brief sound is monitored in a sound-reverberating room, it is immediately followed by numerous echoes bounced off the walls and ceiling. Only the first sound to arrive at the ears appears to be used in its localization. This is generally referred to as the precedence effect. If the processing of verbal information is seen as a reverberating system (after Hebb) and rehearsal as the manifestation of the echoes, then an analogous precedence effect can be empirically demonstrated. Such an analogy not only helps explain previously uninterpretable data but also generates a very unique prediction that was confirmed by experimental data. The theoretical implications of the analogy are also discussed.     

One sound or two? Object-related negativity indexes echo perception

The ability to isolate a single sound source among concurrent sources and reverberant energy is necessary for understanding the auditory world. The precedence effect describes a related experimental finding, that when presented with identical sounds from two locations with a short onset asynchrony (on the order of milliseconds), listeners report a single source with a location dominated by the lead sound. Single-cell recordings in multiple animal models have indicated that there are low-level mechanisms that may contribute to the precedence effect, yet psychophysical studies in humans have provided evidence that top-down cognitive processes have a great deal of influence on the perception of simulated echoes. In the present study, event-related potentials evoked by click pairs at and around listeners' echo thresholds indicate that perception of the lead and lag sound as individual sources elicits a negativity between 100 and 250 msec, previously termed the object-related negativity (ORN). Even for physically identical stimuli, the ORN is evident when listeners report hearing, as compared with not hearing, a second sound source. These results define a neural mechanism related to the conscious perception of multiple auditory objects.     

Sudden changes in spectrum of an echo cause a breakdown of the precedence effect

The effect of changing the frequency components of an echo relative to the sound source was examined in a two-choice discrimination task. Subjects sat in an anechoic chamber and discriminated the direction of the lag noise burst within a lead-lag pair presented over loudspeakers. The leading noise burst was broadband, and the lagging burst was either high- or low-pass filtered. On some conditions, this test burst pair was preceded by a conditioning train of burst pairs, which also had a broadband lead and either a high- or low-frequency lag. When the frequency content of the echo was held constant across the conditioning train and test burst pair, echo suppression that was built up during the repeating train was maintained for the test burst pair, shown by the subjects’ poor performance in detecting the location of the lagging burst. By comparison, subjects had little difficulty in localizing the lagging burst when the frequency content of the echo changed between the conditioning train and the test burst, indicating that any buildup of suppression during the train was broken when the lagging burst’s spectrum shifted. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners’ built-up expectations about room acoustics are violated.     

Echo suppression and discrimination suppression aspects of the precedence effect

The precedence effect is a phenomenon that may occur when a sound from one direction (the lead) is followed within a few milliseconds by the same or a similar sound from another direction (the lag, or the echo). Typically, the lag sound is not heard as a separate event, and changes in the lag sound’s direction cannot be discriminated. The hypothesis is proposed in this study that these two aspects of precedence (echo suppression and discrimination suppression) are at least partially independent phenomena. Two experiments were conducted in which pairs of noise bursts were presented to subjects from two loudspeakers in the horizontal plane to simulate a lead sound and a lag sound (the echo). Echo suppression threshold was measured as the minimum echo delay at which subjects reported hearing two sounds rather than one sound; discrimination suppression threshold was measured as the minimum echo delay at which subjects could reliably discriminate between two positions of the echo. In Experiment 1, it was found that echo suppression threshold was the same as discrimination suppression threshold when measured with a single burst pair (average 5.4 msec). However, when measured after presentation of a train of burst pairs (a condition that may produce “buildup of suppression”), discrimination suppression threshold increased to 10.4 msec, while echo suppression threshold increased to 26.4 msec. The greater buildup of echo suppression than of discrimination suppression indicates that the two phenomena are distinct under buildup conditions and may be the reflection of different underlying mechanisms. Experiment 2 investigated the effect of the directional properties of the lead and lag sounds on discrimination suppression and echo suppression. There was no consistent effect of the spatial separation between lead and lag sources on discrimination suppression or echo suppression, nor was there any consistent difference between the two types of thresholds (overall average threshold was 5.9 msec). The negative result in Experiment 2 may have been due to the measurements being obtained only for single-stimulus conditions and not for buildup conditions that may involve more central processing by the auditory system.     

Hearing Spaces

In this paper I argue that empty space can be heard. This position contrasts with the generally held view that the only things that can be heard are sounds, their properties, echoes, and perhaps sound sources. Specifically, I suggest that when sounds reverberate in enclosed environments we auditorily represent the volume of space surrounding us. Clearly, we can learn the approximate size of an enclosed space through hearing a sound reverberate within it, and so any account that denies that we hear empty space must instead show how beliefs about volumes of space can be derived indirectly from what is heard. That is, if space is not auditorily represented when we hear sounds reverberate, what is? I consider whether hearing reverberation can be thought of as hearing a distinct sound, hearing echoes, or hearing a property of a sound. I argue that experiences of reverberation cannot be reduced to the perception of any of these types and that therefore empty space is represented in auditory perceptual content. In the final section I outline two ways in which space might be represented.     

Effect of click rate and delay on breakdown of the precedence effect

The precedence effect was tested as a function of echo-click delay and click rate after an abrupt switch in location between leading and lagging clicks. Click trains at three rates, 1/sec, 2/sec, and 4/sec, with delays ranging between 2 and 20 msec, were presented to subjects in an anechoic chamber. Duration of the click train after the switch in location was 12 sec, and echo click perceptibility was assessed throughout this period. The number of echo clicks heard was an increasing monotonic function of delay. The subjects reported a "fade-out" of echo clicks after a set number of clicks at each delay, regardless of rate. This result was interpreted as a buildup in inhibition of echoes produced by the ongoing click train. Suppression of echoes was stronger when the leading click originated from the right side than from the left side.     

Effects of Action Video Game Experience on Change Detection

Reflected sounds are often treated as an acoustic problem because they produce false localization cues and decrease speech intelligibility. However, their properties are shaped by the acoustic properties of the environment and therefore are a potential source of information about that environment. The objective of this study was to determine whether information carried by reflected sounds can be used by listeners to enhance their awareness of their auditory environment. Twelve listeners participated in two auditory training tasks in which they learned to identify three environments based on a limited subset of sounds and then were tested to determine whether they could transfer that learning to new, unfamiliar sounds. Results showed that significant learning occurred despite the task difficulty. An analysis of stimulus attributes suggests that it is easiest to learn to identify reflected sound when it occurs in sounds with longer decay times and broadly distributed dominant spectral components.     

The precedence effect in three species of birds (Melopsittacus undulatus, Serinus canaria, and Taeniopygia guttata)

The perceived locations of paired auditory images, simulating direct sounds and their echoes, have been recently studied in budgerigars (Melopsittacus undulatus; M. L. Dent & R. J. Dooling, 2003a, 2003b). In this article, the authors extend those experiments to include measurements of the precedence effect using a discrimination paradigm in two additional bird species: canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). Although time courses of summing localization, localization dominance, and echo thresholds were similar across all species, budgerigars had slightly higher overall levels of discrimination. The results from these experiments add further support that the precedence effect in birds is similar to that found in other animals and that the ability to suppress echoes that might degrade localization and auditory object perception may be a general property of the vertebrate auditory system.     

Stimulus and response repetition effects in the detection of sounds: evidence of obligatory retrieval and use of a prior event

Three experiments were performed to examine the extent to which the time required to detect a probe sound is determined by the acoustic characteristics of a preceding prime sound and by the nature of the response made to the prime. The results of Experiment 1 revealed that the effect of frequency repetition was facilitative when a response was made to the occurrence of both the prime and the probe, but was inhibitory when a response was made only to the probe. In contrast, there was no significant effect of location repetition when responses were made to both prime and probe but there was a strongly inhibitory effect when a response was required only to the probe. These results suggest that the acoustic characteristics of the prime along with information about any response made to it, are used in preparing and executing a response to the probe. Experiment 2 was designed to disrupt the temporal link between prime and probe as a way to discourage such retrieval. The results of the experiment revealed that although a response was required to both the prime and probe, no significant effect of frequency repetition was apparent but a robust inhibitory effect of location repetition emerged. In the third experiment repetition effects both within a trial (i.e., prime to probe) and between trials (i.e., probe to prime) were examined. A facilitative effect of frequency repetition was apparent when the interval between sounds was brief, and an inhibitory effect of location repetition was apparent when the interval between sounds was relatively lengthy. Taken together these results suggest that even simple perceptual judgments may be influenced by retrieval of information about a previous processing episode and that effects of frequency repetition and location repetition may be mediated by different mechanisms.     

Binding “what” and “where” in auditory working memory: An asymmetrical association between sound identity and sound location

Contrasting results in visual and auditory working memory studies suggest that the mechanisms of association between location and identity of stimuli depend on the sensory modality of the input. In this auditory study, we tested whether the association of two features both encoded in the “what” stream is different from the association between a “what” and a “where” feature. In an old–new recognition task, blindfolded participants were presented with sequences of sounds varying in timbre, pitch and location. They were required to judge if either the timbre, pitch or location of a single-probe stimulus was identical or different to the timbre, pitch or location of one of the sounds of the previous sequence. Only variations in one of the three features were relevant for the task, whereas the other two features could vary, with task-irrelevant changes. Results showed that task-irrelevant variations in the “what” features (either timbre or pitch) caused an impaired recognition of sound location and in the other task-relevant “what” feature, whereas changes in sound location did not affect the recognition of either one of the “what” features. We conclude that the identity of sounds is incidentally processed even when not required by the task, whereas sound location is not maintained when task irrelevant.     

Feature mismatch effects in auditory negative priming: interference as dependent on salient aspects of prior episodes

A handful of studies have revealed that withholding a response to a sound causes impaired responding to that sound when subsequently presented (Buchner & Steffens, 2001; Mondor, Leboe, & Leboe, 2005). In the present study, we investigated whether a switch in the location of a repeated sound might represent an additional source of this auditory negative priming effect. In all three of our experiments, participants performed a series of trials in which they withheld a response to a dichotic pair of prime sounds presented to each ear. A dichotic pair of probe sounds was then presented to each ear, and the participants were required to categorize one of them. Across these experiments, the participants were slower to categorize only repeated sounds that were presented in opposite locations.     

Characteristic sounds facilitate visual search

In a natural environment, objects that we look for often make characteristic sounds. A hiding cat may meow, or the keys in the cluttered drawer may jingle when moved. Using a visual search paradigm, we demonstrated that characteristic sounds facilitated visual localization of objects, even when the sounds carried no location information. For example, finding a cat was faster when participants heard a meow sound. In contrast, sounds had no effect when participants searched for names rather than pictures of objects. For example, hearing “meow” did not facilitate localization of the word cat. These results suggest that characteristic sounds cross-modally enhance visual (rather than conceptual) processing of the corresponding objects. Our behavioral demonstration of object-based cross-modal enhancement complements the extensive literature on space-based cross-modal interactions. When looking for your keys next time, you might want to play jingling sounds.     

Feature mismatch effects in auditory negative

A handful of studies have revealed that withholding a response to a sound causes impaired responding to that sound when subsequently presented (Buchner & Steffens, 2001; Mondor, Leboe, & Leboe, 2005). In the present study, we investigated whether a switch in the location of a repeated sound might represent an additional source of this auditory negative priming effect. In all three of our experiments, participants performed a series of trials in which they withheld a response to a dichotic pair of prime sounds presented to each ear. A dichotic pair ofprobe sounds was then presented to each ear, and the participants were required to categorize one of them. Across these experiments, the participants were slower to categorize only repeated sounds that were presented in opposite locations.     

The involuntary capture of attention by novel feature pairings: A study of voice—location integration in auditory sensory memory

Past researchers of the integration of information in memory have typically required participants to attend to and/or commit to memory the stimuli conveying distinct features, rendering difficult the examination of whether the maintenance of the feature pairings can occur involuntarily. To address this issue, the integration of voice and location information in auditory sensory memory was measured using a cross-modal oddball task, in which task-irrelevant auditory deviants are known to capture attention in an involuntary fashion. Participants categorized visual digits presented shortly after to-be-ignored sounds. These sounds consisted in the same phoneme played simultaneously in both ears but in different voices (female in one ear, male in the other). On most trials, the pairing of voice to location was constant (standard sound). On rare and unpredictable trials, the voices swapped locations (deviant sound). In line with past work on attention capture by auditory novelty, the participants were significantly slower to judge the visual digits following the deviant sound, indicating the involuntary encoding of the links between voice and location in auditory memory. These results suggest that voices and locations are integrated in memory and that this binding occurs in conditions in which participants do not intend to commit any information to memory.     

Phonetic recalibration only occurs in speech mode

Upon hearing an ambiguous speech sound dubbed onto lipread speech, listeners adjust their phonetic categories in accordance with the lipread information (recalibration) that tells what the phoneme should be. Here we used sine wave speech (SWS) to show that this tuning effect occurs if the SWS sounds are perceived as speech, but not if the sounds are perceived as non-speech. In contrast, selective speech adaptation occurred irrespective of whether listeners were in speech or non-speech mode. These results provide new evidence for the distinction between a speech and non-speech processing mode, and they demonstrate that different mechanisms underlie recalibration and selective speech adaptation.     

Distraction and facilitation--two faces of the same coin?

Unexpected and task-irrelevant sounds can capture our attention and may cause distraction effects reflected by impaired performance in a primary task unrelated to the perturbing sound. The present auditory-visual oddball study examines the effect of the informational content of a sound on the performance in a visual discrimination task. The informational content was modulated by varying the sound-target interval and the probability of target occurrence. Effects of informational content were examined with two types of distractors: a burst of white noise (deviant) and environmental sounds (novel). Behavioral results reveal the following. (1) Novel and deviant sounds do not necessarily cause behavioral distraction effects when they are uninformative with respect to both time and probability of occurrence of a visual target. (2) Novel, but not deviant, sounds cause an unspecific bias toward facilitation. (3) The informational content of task-irrelevant sounds speeds reaction times, indicating the use of information not directly related to the task for enhancing performance. (4) It is suggested that performance in deviant and novel trials is the sum of the costs of attentional orienting and benefits of information as well as benefits of unspecific activation for novels.     

Visual events modulated by sound in repetition blindness

Repetition blindness (RB; Kanwisher, 1987) is the term used to describe people’s failure to detect or report an item that is repeated in a rapid serial visual presentation (RSVP) stream. Although RB is, by definition, a visual deficit, whether it is affected by an auditory signal remains unknown. In the present study, we added two sounds before, simultaneous with, or after the onset of the two critical visual items during RSVP to examine the effect of sound on RB. The results show that the addition of the sounds effectively reduced RB when they appeared at, or around, the critical items. These results indicate that it is easier to perceive an event containing multisensory information than unisensory ones. Possible mechanisms of how visual and auditory information interact are discussed.     

Auditory spatial negative priming: What is remembered of irrelevant sounds and their locations?

The categorization and identification of previously ignored visual or auditory stimuli is typically slowed down—a phenomenon that has been called the negative priming effect and can be explained by the episodic retrieval of response-inadequate prime information and/or an inhibitory model. A similar after-effect has been found in visuospatial tasks: participants are slowed down in localizing a visual stimulus that appears at a previously ignored location. In the auditory modality, however, such an after-effect of ignoring a sound at a specific location has never been reported. Instead, participants are impaired in their localization performance when the sound at the previously ignored location changes identity, a finding which is compatible with the so-called feature-mismatch hypothesis. Here, we describe the properties of auditory spatial in contrast to visuospatial negative priming and report two experiments that specify the nature of this auditory after-effect. Experiment 1 shows that the detection of identity-location mismatches is a genuinely auditory phenomenon that can be replicated even when the sound sources are invisible. Experiment 2 reveals that the detection of sound-identity mismatches in the probe depends on the processing demands in the prime. This finding implies that the localization of irrelevant sound sources is not the inevitable consequence of processing the auditory prime scenario but depends on the difficulty of the target search process among distractor sounds.     

Lateralization of two-transient stimuli

In this study of the precedence effect in binaural hearing, subjects adjusted the interaural delay of a wideband acoustic pointer to match the perceived intracranial position of transient test stimuli presented over headphones. The test stimuli had leading and lagging components (either brief noise bursts or clicks), each with its own interaural delay. In some test conditions, the leading and lagging stimuli were coherent copies of one another, whereas in others, they were independent samples of noise. The duration of the stimuli and the delay from the leading component to the lagging component were also varied. All the stimulus conditions showed a moderate or strong precedence effect (i.e., covariation of perceived lateral position of the composite two-transient stimulus with the interaural delay of the leading component). Predictions of the lateralization data are presented for variants of models based on temporal weighting and/or bandpass correlation. In one model variant, the binaural stimuli are temporally weighted to emphasize the onset and then subjected to bandpass correlation analysis. In another variant, it is assumed that the onset mechanism provides a rough estimate of the initial interaural delay that guides a slower and more focused bandpass correlation analysis. The accuracies of these two model's predictions were equivalent and superior to those of models that either represent leading and lagging cues equally (bandpass correlation with no onset effect) or do not represent lagging cues at all (a complete precedence effect). The results of these analyses show the need for both a strong onset effect and for bandpass correlation analysis and suggest two modeling approaches for achieving that goal.     

Stimulus expectancy modulates inferior frontal gyrus and premotor cortex activity in auditory perception

In studies on auditory speech perception, participants are often asked to perform active tasks, e.g. decide whether the perceived sound is a speech sound or not. However, information about the stimulus, inherent in such tasks, may induce expectations that cause altered activations not only in the auditory cortex, but also in frontal areas such as inferior frontal gyrus (IFG) and motor cortices, even in the absence of an explicit task. To investigate this, we applied spectral mixes of a flute sound and either vowels or specific music instrument sounds (e.g. trumpet) in an fMRI study, in combination with three different instructions. The instructions either revealed no information about stimulus features, or explicit information about either the music instrument or the vowel features. The results demonstrated that, besides an involvement of posterior temporal areas, stimulus expectancy modulated in particular a network comprising IFG and premotor cortices during this passive listening task.