Biomedical subjects

E William Yund

Publications and source records attributed to E William Yund.

6 recordsLinked to original sources

PubMed2004

Attentional modulation of human auditory cortex.

Attention powerfully influences auditory perception, but little is understood about the mechanisms whereby attention sharpens responses to unattended sounds. We used high-resolution surface mapping techniques (using functional magnetic resonance imaging, fMRI) to examine activity in human auditory cortex during an intermodal selective attention task. Stimulus-dependent activations (SDAs), evoked by unattended sounds during demanding visual tasks, were maximal over mesial auditory cortex. They were tuned to sound frequency and location, and showed rapid adaptation to repeated sounds. Attention-related modulations (ARMs) were isolated as response enhancements that occurred when subjects performed pitch-discrimination tasks. In contrast to SDAs, ARMs were localized to lateral auditory cortex, showed broad frequency and location tuning, and increased in amplitude with sound repetition. The results suggest a functional dichotomy of auditory cortical fields: stimulus-determined mesial fields that faithfully transmit acoustic information, and attentionally labile lateral fields that analyze acoustic features of behaviorally relevant sounds.

Acoustic Stimulation↗

PubMed2004

Local landmark-based mapping of human auditory cortex.

Mammalian sensory cortex is functionally partitioned into cortical fields that are specialized for different processing operations. In theory, averaging functional and anatomical images across subjects can reveal both the average anatomy and the mean functional organization of sensory regions. However, this averaging process must overcome at least two obstacles: (1) the relative locations and sizes of cortical sensory areas vary in different subjects so that across-subject averaging introduces spatial smearing; (2) the relative locations and sizes of cortical areas vary between hemispheres, making it difficult to compare activations between hemispheres or to combine activations across hemispheres. These difficulties are particularly acute for small cortical regions such as auditory cortex. In whole-brain averaging procedures, considerable intersubject variance in the location and orientation of auditory cortex is introduced by variance of the size and shape of structures outside auditory cortex. Here, we compared these global methods with local landmark-based methods (LLMs) that use warping based on local anatomical landmarks. In comparison to maps made with global methods, LLMs produced anatomical maps of auditory cortex with clearer gyral and sulcal structure, and produce functional maps with improved resolution. These results suggest that LLMs have significant advantages over global mapping procedures in studying the details of auditory cortex organization.

Adult↗

PubMed2003

An ERP study of the global precedence effect: the role of spatial frequency.

OBJECTIVE: This study investigated the neural mechanisms underlying the effects of removal of low spatial frequency (SF) contents from stimulus displays on the processing of global and local properties of compound stimuli. METHODS: Event-related brain potentials (ERPs) were recorded from 16 subjects who selectively attended to the global or local features of compound letters, which were either white on a gray background containing broadband SFs or were contrast-balanced (CB) to eliminate low SFs, and were randomly presented in the left or right visual fields. ERPs were analyzed to examine how global/local attention modulations of neural substrates were influenced by SF manipulations. RESULTS: We found that an early process of global recognition was indexed by a negativity peaking at 190 ms over contralateral occipito-temporal cortex and was eliminated by contrast balancing. The late stage of global recognition was reflected in a late negativity peaking at 300 ms and was only retarded by contrast balancing. Global-to-local interference was characterized by enhanced occipito-temporal negativities and was evident for both broadband and CB stimuli. CONCLUSIONS: The results clarify distinct cognitive and neural mechanisms underlying the global precedence and interference effects, which were different in terms of the independence of low SFs in compound stimuli.

Adult↗

PubMed2002

Hemispheric asymmetry in global/local processing: effects of stimulus position and spatial frequency.

We examined the neural mechanisms of functional asymmetry between hemispheres in the processing of global and local information of hierarchical stimuli by measuring hemodynamic responses with functional magnetic resonance imaging (fMRI). In a selective attention task, subjects responded to targets at the global or local level of compound letters that were (1) broadband in spatial-frequency spectrum and presented at fixation; (2) broadband and presented randomly to the left or the right of fixation; or (3) contrast balanced (CB) to remove low spatial frequencies (SFs) and presented at fixation. Central broadband stimuli induced stronger activation in the right middle occipital cortex under global relative to local attention conditions but in the left inferior occipital cortex, stronger activation was induced under local relative to global attention conditions. The asymmetry over the occipital cortex was weakened by unilateral presentation and by contrast balancing. The results indicate that the lateralization of global and local processing is modulated by the position and SF spectrum of the compound stimuli. The global attention also produced stronger activation over the medial occipital cortex relative to the local attention under all the stimulus conditions. The nature of these effects is discussed.

Adult↗

PubMedDate not supplied

Acclimatization in wide dynamic range multichannel compression and linear amplification hearing aids.

Acclimatization was studied in hearing-impaired patients with no previous hearing aid (HA) experience who were fit bilaterally with either wide dynamic range multichannel compression (WDRMCC) or linear amplification (LA) HAs. Throughout 40 weeks of normal HA use, we monitored changes in nonsense syllable perception in speech-spectrum noise. Syllable recognition for WDRMCC users improved by 4.6% over the first 8 weeks, but the 2.2% improvement for LA users was complete in 2 to 4 weeks. Consonant confusion analyses indicated that WDRMCC experience facilitated consonant identification, while LA users primarily changed their response biases. Furthermore, WDRMCC users showed greater improvement for aided than unaided stimuli, while LA users did not. These results demonstrate acclimatization in new users of WDRMCC HAs but not in new users of LA HAs. A switch in amplification type after 32 weeks produced minimal performance change. Thus, acclimatization depended on the type of amplification and the previous amplification experience.

Adaptation, Physiological↗

PubMedDate not supplied

Perceptual training improves syllable identification in new and experienced hearing aid users.

We assessed the effects of perceptual training of syllable identification in noise on nonsense syllable test (NST) performance of new (Experiment 1) and experienced (Experiment 2) hearing aid (HA) users with sensorineural hearing loss. In Experiment 1, new HA users were randomly assigned to either immediate training (IT) or delayed training (DT) groups. IT subjects underwent 8 weeks of at-home syllable identification training and in-laboratory testing, whereas DT subjects underwent identical in-laboratory testing without training. Training produced large improvements in syllable identification in IT subjects, whereas spontaneous improvement was minimal in DT subjects. DT subjects then underwent training and showed performance improvements comparable with those of the IT group. Training-related improvement in NST scores significantly exceeded improvements due to amplification. In Experiment 2, experienced HA users received identical training and testing procedures as users in Experiment 1. The experienced users also showed significant training benefit. Training-related improvements generalized to untrained voices and were maintained on retention tests. Perceptual training appears to be a promising tool for improving speech perception in new and experienced HA users.

Aged↗