Biomedical subjects

Hillel Pratt

Publications and source records attributed to Hillel Pratt.

28 records · Page 2Linked to original sources

PubMed2003

Electrophysiologic correlates of direction and elevation cues for sound localization in the human brainstem.

Our objective was to study the effects of sound source direction and elevation on human brainstem electrical activity associated with sound localization. The subjects comprised 15 normal-hearing and symmetrically hearing adults Auditory brainstem evoked potentials (ABEPs) were recorded from three channels, in response to alternating-polarity clicks, presented at a rate of 21.1/s, at nine virtual spatial locations with different direction and elevation attributes Equivalent dipoles of the binaural interaction components (BICs) of ABEPs were derived by subtracting the response to binaural clicks at each spatial location from the algebraic sum of monaural responses to stimulation of each ear in turn. The BICs included two major components corresponding in latency to the vertex-neck-recorded components V and VI of ABEP. A significant decrease of the first BIC's equivalent dipole magnitude was observed for clicks in the horizontal-frontal position (no elevation) in the midsagittal plane, and for clicks in the left-horizontal (no elevation) and right diagonally above the head (medium elevation) positions in the coronal plane, compared to clicks positioned directly above the head. Significant effects on equivalent dipole latencies of this component were found for front-back positions in the midsagittal plane and left-right positions in the coronal plane, compared to clicks positioned directly above the head. The most remarkable finding was a significant change in equivalent dipole orientations across stimulus conditions. We conclude that the changes in BIC equivalent dipole latency, amplitude and orientation across stimulus conditions reflect differences in the distribution of binaural pontine activity evoked by sounds in different spatial locations.

Adult↗

PubMed2002

Sound localization in patients with cochlear implant--preliminary results.

OBJECTIVES: To evaluate sound localization ability in patients with unilateral cochlear implant, who do not wear a hearing aid on the contralateral ear, and to try to improve this ability by training. SETTING: Tertiary academic referral center. METHODS: In the initial test, patients were exposed to sound stimuli from different directions and were asked to localize them. Following a training period the patients were re-evaluated by the same test. For each test, the percentage of correct answers and the final test score were calculated. RESULTS: In the initial test, the mean score of the study group of four cochlear implant users was 42.8 (out of a maximal score of 100), the mean rate of correct responses was 27.5%. Following a training period (6.5 sessions on the average), on the final test the mean score of the group was 74.3, while the mean rate of correct responses was 66.5%. CONCLUSIONS: The results demonstrated that patients with unilateral cochlear implant have some ability to localize sound, and that this ability may be improved by regular training.

Adolescent↗

PubMed2002

Electrophysiological evidence for priming in response to words and pseudowords in first and second language.

The study purpose was to indicate when language-specific processing first occurs and how first and second language priming processes interact. Event-related potentials were recorded from 14 normal native Hebrew speakers, in a variation of lexical decision task, to pairs of stimuli (S1, S2) in Hebrew, English, Hebrew pseudowords, and English pseudowords. Although no behavioral priming was observed, priming by pseudowords in either language affected both N400 and the late positive component of event related potential. N1 and P2 latencies were longer to S2 in semantically related pairs, indicating that language-specific processing may take place as early as auditory cortex. Different processing of first and second language was evident only in response to pseudowords.

Adolescent↗

PubMed2002

A comparison of sentence- and discourse-level semantic processing: an ERP study.

Eighteen subjects listened to sentences ending with semantically congruent or incongruent words. Each congruent sentence was embedded at the end of a short story so that the final word was semantically acceptable at the sentence level but incongruent in terms of discourse context. The same stories were also presented with congruent endings. Auditory ERPs elicited by the final words in these sentences and stories were compared. Both sentence- and discourse-level semantic integration were associated with N400 and Late Positive Component (LPC) effects in addition to a new component, P550. Local and global semantic processing, although evoking the same components, were characterized by differential effects on ERP amplitudes according to the amount of text integrated and its congruence. These results indicate similar cognitive processes of context build up, underlying sentence- and discourse-semantic processing.

Adolescent↗

PubMed2002

Band-pass specific contributions of multiple generators to the auditory 40-Hz steady state potentials.

OBJECTIVE: The purpose of this study was to separate the composite components of the auditory 40 Hz steady-state potentials (40 Hz SSP), by differentially augmenting them with filtering at different low passes, and to compare them with their counterparts in the transient-evoked auditory middle-latency evoked potentials (AMEP). METHODS: Transient-evoked AMEP to 3.3/sec clicks and 40 Hz SSP to 40/sec clicks were recorded from 18 subjects using three orthogonally positioned electrode pairs. Each type of potentials was filtered with a 100 Hz and with a 50 Hz low pass. Equivalent dipoles of components were estimated using Three-channel Lissajous' Trajectories and compared between filter settings (50 and 100 Hz low pass) and between the transient-evoked and the steady-state potentials. RESULTS: With a band pass of 3 to 100 each period of the 40 Hz SSP consisted of a brain stem (V) and four cortical (P0 Na, Pa1 Pa2, and Nb) components. The lower-frequency components of the 40-Hz response corresponded in latency and equivalent dipole orientation to the later transient-evoked cortical AMEP components, whereas the higher-frequency components corresponded to the earlier, brain stem and primary cortical components of transient-evoked AMEP. Band-pass filtering at 3 to 50 Hz resulted in fewer components, as early brain stem and primary cortical components diminished. CONCLUSIONS: A band pass of 3 to 100 Hz for recording the 40 Hz SSP results in a composite waveform comprising of distinct brain stem and cortical generators with different orientations of their equivalent dipoles. The relative contributions of the multiple constituents are affected by the acquisition filter low pass: brain stem and primary cortical generators mostly contribute the high frequencies and later cortical contributions dominate the lower frequencies.

Acoustic Stimulation↗

PubMed2002

Time course of auditory cortex activation during speech processing.

The purpose of the studies summarized in this report was to determine the time course of auditory cortex involvement in speech and language processing in the context of auditory object formation. Forty-one subjects took part in the three studies summarized in this report. In all three studies, subjects performed a choice-reaction task that required their pressing an appropriate button in response to auditory stimuli (speech/non-speech, good/worse fused phonemes, first/second language words) presented through earphones. Event-related potentials (ERPs) were recorded during performance of the task from 21 scalp electrodes, in addition to peri-ocular electrodes for monitoring eye movements. Current densities within the gray matter of the brain were estimated using the LORETA (low resolution electromagnetic tomography) method. In general, except for some periods, processing phonetic and linguistic information was associated with elevated activity in the left auditory cortex. Peaks in auditory cortex activation corresponded in time to scalp recorded peaks in the latencies of P1 and up to as late as P3. The adjacent posterior temporal areas showed a similar temporal pattern of activation, but tended to be less lateralized to the left, or even biased toward right hemisphere predominance, depending on the stimulus, particularly in the later time frames. The results indicate that the auditory cortex is engaged in auditory processing from its early stages and as long as a few hundreds of msec, even after cessation of the stimulus, defining sounds as distinct auditory objects and differentiating speech from non-speech material, relying on acoustic cues. Hemispheric dominance fluctuates to include activity in the 'non-dominant' hemisphere depending on stimulus type and stage of processing.

Acoustic Stimulation↗

PubMed2002

Automatic and controlled verbal-information processing in patients with frontal lobe lesions.

The selectivity of frontal lobe lesion effects in the domains of verbal-information processing has not been well established. The authors hypothesized that capacity-limited controlled processing would be more impaired than automatic processing in frontal lobe patients (FLPs). Fifteen FLPs were compared with 2 matched control groups: 14 posterior-lesion patients and 15 normal controls. Both behavioral and event-related brain potential (ERP) measures were collected. Results suggest that both automatic and controlled processing were affected by frontal lobe lesions. ERP results indicated that the main dificulty for the FLPs was in the perceptual stage of information processing. This rather unexpected result may be explained by a basic difficulty of FLPs in attending to a new stimulus in order to process it.

Adult↗

PubMed2002

Distractibility after frontal lobe lesions: behavioral and event-related brain potential evidence.

The authors used a semantic priming paradigm to investigate the distractibility phenomenon of patients with frontal lobe lesions (FLPs). They tested two distractibility categories: an inhibition category requiring inhibition of an automatic response and a distraction category caused by irrelevant, unexpected stimuli. Fifteen FLPs were compared with 2 matched control groups: 14 posterior-lesion patients and 15 normal controls. Both behavioral and event-related brain potential (ERP) measures were used. The results suggest that, although there were differences in performance between the FLP group and the control groups, there was no evidence that the FLPs had difficulty specifically with the inhibition category. The most consistent ERP result was that the FLP group had longer N100 latencies than either control group. On the basis of these results, the authors hypothesize that FLPs have difficulty focusing on and starting to process a new stimulus. The authors also discuss the unique contribution ERP evidence has made to cognitive studies.

Adult↗

PubMedDate not supplied

Promoting Arab and Israeli cooperation: peacebuilding through health initiatives.

This article describes a positive experience in building Arab and Israeli cooperation through health initiatives. Over the past 10 years Israeli, Jordanian, and Palestinian health professionals have worked together through the Canada International Scientific Exchange Program (CISEPO). In the initial project, nearly 17,000 Arab and Israeli newborn babies were tested for early detection of hearing loss, an important health issue for the region. The network has grown to address additional needs, including mother-child health, nutrition, infectious diseases, and youth health. Our guiding model emphasises two goals: project-specific outcomes in health improvement, and broader effects on cross-border cooperation. Lessons learned from this experience and the model provide direction for ways that health professionals can contribute to peacebuilding.

Canada↗

PubMedDate not supplied

Auditory event-related potentials during phonetic and semantic processing in children.

This study was designed to follow the time course of different levels of linguistic processing using auditory event-related potentials (AERPs). A hierarchical set of acoustically controlled stimuli was used to elicit AERPs in 20 normal children who performed discrimination tasks involving pure tones, phonetic 'easy' and 'difficult' stimuli and semantic stimuli. Results show that (1) AERP latencies were similar for phonetic 'easy' and 'difficult' stimuli, (2) prolonged P(2), N(2) and P(3) latencies characterized semantic processing compared to phonetic processing, (3) a late negativity was elicited during semantic processing only, (4) P(3) amplitudes were larger over the left compared to right scalp during linguistic processing (phonetic and semantic) but were similar during nonlinguistic processing (pure tones) and (5) reaction time was found to be longest for semantic processing whereas performance accuracy was found to be an insensitive measure. These results provide insight into brain processes underlying the perception of speech. Furthermore, they support a dual model of speech perception that includes parallel and serial processing.

Adolescent↗