Biomedical subjects

Elyse Sussman

Publications and source records attributed to Elyse Sussman.

18 recordsLinked to original sources

PubMed2006

Object representation in the human auditory system.

One important principle of object processing is exclusive allocation. Any part of the sensory input, including the border between two objects, can only belong to one object at a time. We tested whether tones forming a spectro-temporal border between two sound patterns can belong to both patterns at the same time. Sequences were composed of low-, intermediate- and high-pitched tones. Tones were delivered with short onset-to-onset intervals causing the high and low tones to automatically form separate low and high sound streams. The intermediate-pitch tones could be perceived as part of either one or the other stream, but not both streams at the same time. Thus these tones formed a pitch 'border' between the two streams. The tones were presented in a fixed, cyclically repeating order. Linking the intermediate-pitch tones with the high or the low tones resulted in the perception of two different repeating tonal patterns. Participants were instructed to maintain perception of one of the two tone patterns throughout the stimulus sequences. Occasional changes violated either the selected or the alternative tone pattern, but not both at the same time. We found that only violations of the selected pattern elicited the mismatch negativity event-related potential, indicating that only this pattern was represented in the auditory system. This result suggests that individual sounds are processed as part of only one auditory pattern at a time. Thus tones forming a spectro-temporal border are exclusively assigned to one sound object at any given time, as are spatio-temporal borders in vision.

Acoustic Stimulation↗

PubMed2006

Neurophysiological evidence for context-dependent encoding of sensory input in human auditory cortex.

Attention biases the way in which sound information is stored in auditory memory. Little is known, however, about the contribution of stimulus-driven processes in forming and storing coherent sound events. An electrophysiological index of cortical auditory change detection (mismatch negativity [MMN]) was used to assess whether sensory memory representations could be biased toward one organization over another (one or two auditory streams) without attentional control. Results revealed that sound representations held in sensory memory biased the organization of subsequent auditory input. The results demonstrate that context-dependent sound representations modulate stimulus-dependent neural encoding at early stages of auditory cortical processing.

Acoustic Stimulation↗

PubMed2006

Loudness summation and the mismatch negativity event-related brain potential in humans.

Abstract Infrequently omitting a sound from a repetitive sequence elicits the mismatch negativity (MMN) ERP response when the stimulus onset asynchrony (SOA) is less than 200 ms. We contrasted two alternative explanations of omission MMN. (1) Each sound starts a separate temporal integration process. Omissions violate the constancy of the temporal structure within the integration window. (2) Sounds preceding an omission are perceived to be louder than those followed by a sound within the integration period, because omissions allow the full stimulus aftereffect to be included in perceived loudness. We varied the SOA between 117 and 217 ms. For this case, the temporal structure explanation predicts that no MMN will be elicited, whereas the loudness summation explanation predicts that MMN will be elicited. MMN was elicited by tone omissions with random SOA, suggesting that loudness summation plays an important role in the elicitation of omission MMN.

Acoustic Stimulation↗

PubMed2005

The development of the length of the temporal window of integration for rapidly presented auditory information as indexed by MMN.

OBJECTIVE: The length of the temporal window integrating successive auditory stimuli into unitary percepts has been estimated to be less than 200 ms in adults. The aim of the study was to investigate the development of the integrating window in children to determine whether it is similar to young adults. METHODS: A modified auditory oddball paradigm was presented at a rapid (150-400 ms) onset-to-onset pace during recording of electroencephalogram in two groups of children (aged 5-8 and 9-11 years) and one group of adults. Latencies and amplitudes of the P1, N1, and the mismatch negativity (MMN) components of event-related brain potentials (ERPs) were measured. RESULTS: The length of the temporal window of integration (TWI) was shorter in adults (<200 ms) than older children (<300 ms in 9-11-year-olds) and younger children (<350 ms in the 5-8-year-olds). In addition, age-related changes were found in the latency and amplitude of the ERP components. CONCLUSIONS: The results demonstrate a general maturational development of the auditory evoked potentials and also a specific maturational process for temporal encoding of information in auditory cortex. SIGNIFICANCE: Rapid stimulus presentation rates can be successfully used in school-aged children to study neural mechanisms of auditory processes.

Acoustic Stimulation↗

PubMed2005

Event-related brain potentials reveal multiple stages in the perceptual organization of sound.

Auditory stream segregation has been suggested to include two distinct processing stages: (1) forming representations for alternative organizations of the acoustic input and (2) choosing one organization for perception after weighing the evidence that supports the different alternatives. The current study tested the possibility that auditory event-related potentials (ERP) could be used to index both stages of the stream-segregation process. Sequences of tones that could be perceived either as a single coherent auditory stream (integrated organization) or as two separate streams of sounds (segregated organization) were presented to subjects. The stimulus configuration encouraged perception to fluctuate between these alternative organizations. Subjects were instructed to continuously indicate whether they perceived one or the other organization of the tone sequence. Occasionally, a tone was omitted from the otherwise regular sequence. This deviance was expected to be processed differently depending on the perceptual organization of the sequence at the time of the omission. We found an early ERP response to omission, which was fully determined by parameters of the stimulation and was not sensitive to the perceived sound organization. In contrast, modulation of two ERP components elicited by the regular tone patterns as well as later responses elicited by deviants correlated with the perceived sound organization. These results suggest that sound organization goes through at least two distinct stages, the first being fully stimulus driven, whereas the second is partly under top-down control.

Adult↗

PubMed2005

Preattentive binding of auditory and visual stimulus features.

We investigated the role of attention in feature binding in the auditory and the visual modality. One auditory and one visual experiment used the mismatch negativity (MMN and vMMN, respectively) event-related potential to index the memory representations created from stimulus sequences, which were either task-relevant and, therefore, attended or task-irrelevant and ignored. In the latter case, the primary task was a continuous demanding within-modality task. The test sequences were composed of two frequently occurring stimuli, which differed from each other in two stimulus features (standard stimuli) and two infrequently occurring stimuli (deviants), which combined one feature from one standard stimulus with the other feature of the other standard stimulus. Deviant stimuli elicited MMN responses of similar parameters across the different attentional conditions. These results suggest that the memory representations involved in the MMN deviance detection response encoded the frequently occurring feature combinations whether or not the test sequences were attended. A possible alternative to the memory-based interpretation of the visual results, the elicitation of the McCollough color-contingent aftereffect, was ruled out by the results of our third experiment. The current results are compared with those supporting the attentive feature integration theory. We conclude that (1) with comparable stimulus paradigms, similar results have been obtained in the two modalities, (2) there exist preattentive processes of feature binding, however, (3) conjoining features within rich arrays of objects under time pressure and/or longterm retention of the feature-conjoined memory representations may require attentive processes.

Acoustic Stimulation↗

PubMed2004

Auditory organization of sound sequences by a temporal or numerical regularity--a mismatch negativity study comparing musicians and non-musicians.

The human auditory system can encode regularities in the acoustic environment without the requirement of attention. We investigated whether the auditory system of musicians is more sensitive than that of non-musicians in encoding complex regularities. We presented tone sequences containing either a temporal or a numerical regularity. The sequence with the temporal regularity could be divided into segments of a constant duration while the segments contained a varying number of tones. The sequence with the numerical regularity, on the other hand, could be divided into segments containing a constant number of tones while the segments varied in duration. Auditory encoding of the regularity was determined by measuring whether an occasional segment lengthening, either in time or by number elicited the mismatch negativity (MMN). In both musicians and non-musicians, an MMN was elicited when the temporal regularity was violated. In contrast, only in musicians an MMN was elicited to violations of the numerical regularity. The results show that temporal processing is of general importance in audition since at an involuntary auditory processing stage a complex temporal regularity can be encoded irrespective of musical expertise. Furthermore, the auditory system of professional musicians can encode a numerical regularity without attention being required reflecting the functional importance of beat tracking in the perceptual organization of music.

Adult↗

PubMed2004

Pre-attentive categorization of vowel formant structure in complex tones.

It has been demonstrated that vowel information can be extracted from speech sounds without attention focused on them, despite widely varying non-speech acoustic information in the input. The present study tested whether even complex tones that were constructed based on F0, F1 and F2 vowel frequencies to resemble the defining features of speech sounds, but were not speech, are categorized pre-attentively according to vowel space information. The Mismatch Negativity brain response was elicited by infrequent tokens of the complex tones, showing that the auditory system can pre-attentively categorize speech information on the basis of the minimal, defining auditory features. The human mind extracts the language-relevant information from complex tones despite the non-relevant variation in the sound input.

Adult↗

PubMed2004

Automatic and controlled processing of acoustic and phonetic contrasts.

Changes in the temporal properties of the speech signal provide important cues for phoneme identification. An impairment or inability to detect such changes may adversely affect one's ability to understand spoken speech. The difference in meaning between the Finnish words tuli (fire) and tuuli (wind), for example, lies in the difference between the duration of the vowel /u/. Detecting changes in the temporal properties of the speech signal, therefore, is critical for distinguishing between phonemes and identifying words. In the current study, we tested whether detection of changes in speech sounds, in native Finnish speakers, would vary as a function of the position within the word that the informational changes occurred (beginning, middle, or end) by evaluating how length contrasts in segments of three-syllable Finnish pseudo-words and their acoustic correlates were discriminated. We recorded a combination of cortical components of event-related brain potentials (MMN, N2b, P3b) along with behavioral measures of the perception of the same sounds. It was found that speech sounds were not processed differently than non-speech sounds in the early stages of auditory processing indexed by MMN. Differences occurred only in later stages associated with controlled processes. The effects of position and attention on speech and non-speech stimuli are discussed.

Acoustic Stimulation↗

PubMed2004

Grouping of sequential sounds--an event-related potential study comparing musicians and nonmusicians.

It is believed that auditory processes governing grouping and segmentation of sounds are automatic and represent universal aspects of music perception (e.g., they are independent of the listener's musical skill). The present study challenges this view by showing that musicians and nonmusicians differ in their ability to preattentively group consecutive sounds. We measured event-related potentials (ERPs) from professional musicians and nonmusicians who were presented with isochronous tone sequences that they ignored. Four consecutive tones in a sequence could be grouped according to either pitch similarity or good continuation of pitch. Occasionally, the tone-group length was violated by a deviant tone. The mismatch negativity (MMN) was elicited to the deviants in both subject groups when the sounds could be grouped based on pitch similarity. In contrast, MMN was only elicited in musicians when the sounds could be grouped according to good continuation of pitch. These results suggest that some forms of auditory grouping depend on musical skill and that not all aspects of auditory grouping are universal.

Acoustic Stimulation↗

PubMed2003

Human auditory cortex tracks task-irrelevant sound sources.

The brain organizes sound into coherent sequences, termed auditory streams. We asked whether task-irrelevant sounds would be detected as separate auditory streams in a natural listening environment that included three simultaneously active sound sources. Participants watched a movie with sound while street-noise and sequences of naturally varying footstep sounds were presented in the background. Occasional deviations in the footstep sequences elicited the mismatch negativity (MMN) event-related potential. The elicitation of MMN showed that the regular features of the footstep sequences had been registered and their violations detected, which could only occur if the footstep sequence had been detected as a separate auditory stream. Our results demonstrate that sounds are organized into auditory streams irrespective of their relevance to ongoing behavior.

Acoustic Stimulation↗

PubMed2003

Newborn infants can organize the auditory world.

The perceptual world of neonates is usually regarded as not yet being fully organized in terms of objects in the same way as it is for adults. Using a recently developed method based on electric brain responses, we found that, similarly to adults, newborn infants segregate concurrent streams of sound, allowing them to organize the auditory input according to the existing sound source. The segregation of concurrent sound streams is a crucial step in the path leading to the identification of objects in the environment. Its presence in newborn infants shows that the basic abilities required for the development of conceptual objects are available already at the time of birth.

Adult↗

PubMed2003

MMN and attention: competition for deviance detection.

We addressed the question of whether the mismatch negativity (MMN) event-related potential reflects an attention-independent process. Previous studies have shown that the MMN response to intensity deviation was significantly reduced or even abolished when attention was highly focused on a concurrent sound channel, whereas no conclusive evidence of attentional sensitivity has been obtained for frequency deviation. We tested a new hypothesis suggesting that competition between detection of identical deviations in attended and unattended channels and the biasing of this competition induced by the subject's task account for the observed MMN effects. In a fast-paced dichotic paradigm, we set up competition for frequency MMN and removed it for intensity MMN. We found that frequency MMN was now abolished in the unattended channel, whereas the amplitude of the intensity MMN was unaffected. These results support the competition hypothesis and suggest that selective attention in and of itself does not affect the MMN. Top-down processes can determine what information reaches the deviance-detection process when changes in multiple channels vie for the same MMN resource and one of the competing changes is relevant for the subject's task.

Acoustic Stimulation↗

PubMed2003

Representation of the standard: stimulus context effects on the process generating the mismatch negativity component of event-related brain potentials.

In the auditory oddball paradigm, the frequent occurrence of a sound (the "standard") forms the basis of deviance detection. The incoming sounds are compared with the cortical representation of the standard and those sounds that do not match it elicit the mismatch negativity (MMN) event-related brain potential. Here we address the issue of whether the relative probability of the sounds in a sequence was a critical factor influencing which sounds would be represented as standards in the deviant comparison process. One frequent (F1) and two infrequent (D1 and D2) sounds that differed only in duration were presented in a sequence. D1 occurred proportionally as frequently with respect to D2 as F1 occurred with respect to D1. If the proportional relationship of sounds were critical then D1 could serve as a "standard" to D2 and thus D2 should elicit two MMNs. However, D2 elicited MMN only with respect to F1. This result as well as those obtained in two control conditions suggests that "standards" are not established on the basis of relative probability; they emerge as a result of global characteristics, the longer-term context, of the sound sequence.

Acoustic Stimulation↗

PubMed2003

Preattentive auditory context effects.

The effects of auditory context on the preattentive and perceptual organization of tone sequences were investigated. Two sets of experiments were conducted in which the pitch of contextual tones was varied, bringing about two different contextual manipulations. Preattentive auditory organization was indexed by the mismatch negativity event-related potential, which is elicited by violations of auditory regularities even when participants ignore the sounds (e.g., by reading a book). The perceptual effects of the contextual manipulations on auditory grouping were assessed using target-detection and order-judgment tasks. The close correspondence found between the effects of auditory context on the perceptual and preattentive measures of auditory grouping suggests that a large part of contextual processing is preattentive.

Acoustic Stimulation↗

PubMed2002

Top-down effects can modify the initially stimulus-driven auditory organization.

We recorded event-related potentials (ERPs) and magnetic fields (ERFs) of the human brain to determine whether top-down control could modulate the initial organization of sound representations in the auditory cortex. We presented identical sound stimulation and manipulated top-down processes by instructing participants to either ignore the sounds (Ignore condition), to detect pitch changes (Attend-pitch condition), or to detect violations of a repeating tone pattern (Attend-pattern condition). The ERP results obtained in the Attend-pattern condition dramatically differed from those obtained with the other two task instructions. The magnetoencephalogram (MEG) findings were fully compatible, showing that the neural populations involved in detecting pattern violations differed from those involved in detecting pitch changes. The results demonstrate a top-down effect on the sound representation maintained in auditory cortex.

Acoustic Stimulation↗

PubMed2002

Temporal integration: intentional sound discrimination does not modulate stimulus-driven processes in auditory event synthesis.

OBJECTIVE: Our previous study showed that the auditory context could influence whether two successive acoustic changes occurring within the temporal integration window (approximately 200ms) were pre-attentively encoded as a single auditory event or as two discrete events (Cogn Brain Res 12 (2001) 431). The aim of the current study was to assess whether top-down processes could influence the stimulus-driven processes in determining what constitutes an auditory event. METHODS: Electroencepholagram (EEG) was recorded from 11 scalp electrodes to frequently occurring standard and infrequently occurring deviant sounds. Within the stimulus blocks, deviants either occurred only in pairs (successive feature changes) or both singly and in pairs. Event-related potential indices of change and target detection, the mismatch negativity (MMN) and the N2b component, respectively, were compared with the simultaneously measured performance in discriminating the deviants. RESULTS: Even though subjects could voluntarily distinguish the two successive auditory feature changes from each other, which was also indicated by the elicitation of the N2b target-detection response, top-down processes did not modify the event organization reflected by the MMN response. CONCLUSIONS: Top-down processes can extract elemental auditory information from a single integrated acoustic event, but the extraction occurs at a later processing stage than the one whose outcome is indexed by MMN. SIGNIFICANCE: Initial processes of auditory event-formation are fully governed by the context within which the sounds occur. Perception of the deviants as two separate sound events (the top-down effects) did not change the initial neural representation of the same deviants as one event (indexed by the MMN), without a corresponding change in the stimulus-driven sound organization.

Acoustic Stimulation↗

PubMed2002

Memory reactivation or reinstatement and the mismatch negativity.

Previous studies have suggested that the memory underlying the mismatch negativity (MMN) can be deactivated by a period of silence and later reactivated. An alternative is that the memory becomes inapplicable due to a period of silence and subsequently reinstated. Both interpretations rest on the absence of a MMN for a deviant in Position 1 of a train (showing deactivation or inapplicability of the memory) and the presence of a MMN in Position 2 of the train (evidencing reactivation or reinstatement of the memory). In these studies, the standards were fixed across all trains of a given condition. Hence, it is not clear if the MMN elicited in Position 2 requires presentation of multiple trains with identical standards or only a single train. Experiment 1 showed that a single train is sufficient. With data from recent studies, Experiment 2 showed that MMNs in Position 2 of trains are due to reinstatement rather than reactivation of the memory.

Acoustic Stimulation↗