Stimulus-based and task-based attention modulate auditory stream segregation context effects.

Previous studies have shown that perceptual segregation increases after listening to longer tone sequences, an effect known as buildup. More recently, an effect of prior frequency separation (Δ) has been discovered: presenting tone sequences with a small Δ biases following sequences with an intermediate Δ to be segregated into two separate streams, whereas presenting context sequences with a large Δ biases following sequences to be integrated into one stream. Here we investigated how attention and task demands influenced these effects of prior stimuli by having participants perform one of three tasks during the context: making streaming judgments on the tone sequences, detecting amplitude modulation in the tones, and performing a visual task while ignoring the tones.

Evidence for high-level feature encoding and persistent memory during auditory stream segregation.

A test sequence of alternating low-frequency (A) and high-frequency (B) tones in a repeating ". . .

Preliminary evidence for reduced auditory lateral suppression in schizophrenia.

Background: Well-documented auditory processing deficits such as impaired frequency discrimination and reduced suppression of auditory brain responses in schizophrenia (SZ) may contribute to abnormal auditory functioning in everyday life. Lateral suppression of non-stimulated neurons by stimulated neurons has not been extensively assessed in SZ and likely plays an important role in precise encoding of sounds. Therefore, this study evaluated whether lateral suppression of activity in auditory cortex is impaired in SZ.

Effects of attention to and awareness of preceding context tones on auditory streaming.

This study determined whether facilitation of auditory stream segregation could occur when facilitating context tones are accompanied by other sounds. Facilitation was measured as the likelihood of a repeated context tone that could match the low (A) or high (B) frequency of a repeating ABA test to increase the likelihood of hearing the test as segregated. We observed this type of facilitation when matching tones were alone, or with simultaneous bandpass noises or continuous speech, neither of which masked the tones.

Loss and persistence of implicit memory for sound: evidence from auditory stream segregation context effects.

An important question is the extent to which declines in memory over time are due to passive loss or active interference from other stimuli. The purpose of the present study was to determine the extent to which implicit memory effects in the perceptual organization of sound sequences are subject to loss and interference. Toward this aim, we took advantage of two recently discovered context effects in the perceptual judgments of sound patterns, one that depends on stimulus features of previous sounds and one that depends on the previous perceptual organization of these sounds.

Evidence for stimulus-general impairments on auditory stream segregation tasks in schizophrenia.

Background: Auditory impairments in schizophrenia have been demonstrated previously, especially for tasks requiring precise encoding of frequency, although it is unclear the extent to which they have difficulty using pitch information and other cues to segregate sounds. We determined the extent to which those with schizophrenia have difficulty using pitch information and other auditory cues to segregate sounds that are presented sequentially.

Methods: Ten participants with schizophrenia and nine healthy/normal control participants completed a battery of tasks that tested for the ability to perform sequential auditory stream segregation using pitch, amplitude modulation, or inter-aural phase difference as cues to segregation.

Auditory stream segregation impairments in schizophrenia.

We used behavior and event-related potentials (ERPs) to examine auditory stream segregation in people with schizophrenia and control participants. During each trial, a context pattern was presented, consisting of low (A) and high (B) tones and silence (-) in a repeating ABA- pattern, with a frequency separation (Δf) of 3, 6, or 12 semitones. Next, a test ABA-pattern was presented that always had a 6-semitone Δf.

Attention, awareness, and the perception of auditory scenes.

Auditory perception and cognition entails both low-level and high-level processes, which are likely to interact with each other to create our rich conscious experience of soundscapes. Recent research that we review has revealed numerous influences of high-level factors, such as attention, intention, and prior experience, on conscious auditory perception. And recently, studies have shown that auditory scene analysis tasks can exhibit multistability in a manner very similar to ambiguous visual stimuli, presenting a unique opportunity to study neural correlates of auditory awareness and the extent to which mechanisms of perception are shared across sensory modalities.

Pattern specificity in the effect of prior Δƒ on auditory stream segregation.

During repeating sequences of low (A) and high (B) tones, perception of two separate streams ("streaming") increases with greater frequency separation (Δƒ) between the A and B tones; in contrast, a prior context with large Δƒ results in less streaming during a subsequent test pattern. The purpose of the present study was to investigate what aspects of the context pattern are necessary for this context effect to occur. Simply changing the B-tone frequency without an alternating A tone present was not sufficient to cause the effect of prior Δƒ, but rather a melodic change between A and B tones was necessary.

Effects of prior stimulus and prior perception on neural correlates of auditory stream segregation.

We examined whether effects of prior experience are mediated by distinct brain processes from those processing current stimulus features. We recorded event-related potentials (ERPs) during an auditory stream segregation task that presented an adaptation sequence with a small, intermediate, or large frequency separation between low and high tones (Deltaf), followed by a test sequence with intermediate Deltaf. Perception of two streams during the test was facilitated by small prior Deltaf and by prior perception of two streams and was accompanied by more positive ERPs.