David M. Weintraub

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. Research has also led to a growing number of techniques through which auditory perception can be manipulated and even completely suppressed. Such findings have important consequences for our understanding of the mechanisms of perception and also should allow scientists to precisely distinguish the influences of different higher-level influences.

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. The scalp topography of these perception-related changes in ERPs was different from that observed for ERP modulations due to increasing the current Deltaf. These results reveal complex interactions between stimulus-driven activity and temporal-context-based processes and suggest a complex set of brain areas involved in modulating perception based on current and previous experience.

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. Larger Δf during the context resulted in more perception of two streams and larger N1 and P2 ERPs, but less perception of two streams during the test pattern. These effects of Δf were smaller in schizophrenia. Individuals with schizophrenia also showed a reduced effect of prior perceptual judgments. Overall, the findings demonstrate that people with schizophrenia have abnormalities in segregating sounds. These abnormalities result from difficulties utilizing frequency cues in addition to reduced temporal context effects.

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. RESULTS All three sequential segregation tasks showed reduced tendency for those with schizophrenia to perceive segregated sounds, compared to control participants. CONCLUSIONS These findings extend prior research by demonstrating a general impairment on sequential sound segregation tasks in schizophrenia, and not just on tasks that require precise encoding of frequency. Together, the pattern of results provide evidence that auditory impairments in schizophrenia result from selective abnormalities in neural circuits that carry out specific computations necessary for stream segregation, as opposed to an impairment in processing specific cues.

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. The experiments measured how listeners’ perceptual organization of a tone sequence (test) was influenced by the frequency separation, or the perceptual organization, of the two preceding sequences (context1 and context2). The results demonstrated clear evidence for loss of context effects over time but little evidence for interference. However, they also revealed that context effects can be surprisingly persistent. The robust effects of loss, followed by persistence, were similar for the two types of context effects. We discuss whether the same auditory memories might contain information about basic stimulus features of sounds (i.e., frequency separation), as well as the perceptual organization of these sounds.

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. METHODS SZ participants and control participants watched a silent movie with subtitles while listening to trials composed of a 0.5s control stimulus (CS), a 3s filtered masking noise (FN), and a 0.5s test stimulus (TS). The CS and TS were identical on each trial and had energy corresponding to the high energy (recurrent suppression) or low energy (lateral suppression) portions of the FN. Event-related potentials were recorded and suppression was measured as the amplitude change between CS and TS. RESULTS Peak amplitudes of the auditory P2 component (160-260ms) showed reduced lateral but not recurrent suppression in SZ participants. CONCLUSIONS Reduced lateral suppression in SZ participants may lead to overlap of neuronal populations representing different auditory stimuli. Such imprecise neural representations may contribute to the difficulties SZ participants have in discriminating complex stimuli in everyday life.