Biomedical subjects

D P Phillips

Publications and source records attributed to D P Phillips.

At least 55 records · Page 3Linked to original sources

PubMed1993

Disturbed speech intelligibility in noise despite a normal audiogram: a defect in temporal resolution?

Patients with complaints of disturbed speech intelligibility in noise, despite normal standard audiograms, constitute a unique yet not uncommon population of listeners. The literature on this patient group is reviewed, and the term Idiopathic Discriminatory Dysfunction (IDD) is introduced in an attempt to standardize and qualify the distinct characteristics of this entity. Preliminary studies of these patients have hypothesized both frequency and temporal resolution deficits underlying this impairment. A representative group of 15 patients suffering from IDD were tested using a new speech-in-noise paradigm designed to test temporal resolution. These patients were found to have near-normal temporal resolving capacity as determined by this task.

Adult↗

PubMed1993

Adequacy of official suicide statistics for scientific research and public policy.

Many researchers have claimed that the study of suicide and the formation of public policy are not undermined by the misclassification of suicide as other causes of death. We evaluated this claim using a new technique and causes of death not previously considered. We examined computerized California death certificates, 1966-1990. Mortality peaks at symbolic ages are a characteristic feature of suicide. We sought such peaks in (1) causes of death commonly suspected of containing misclassified suicides (e.g., accidental barbiturate poisoning), (2) causes of death not hitherto suspected (e.g., pedestrian deaths), and (3) control groups. The first two categories displayed peaks at symbolic ages, but control groups did not. The size of the peak, indicative of misclassified suicides, varied markedly by race (p < .0001) and sex (p < .0001). Misclassification is evident for all time periods examined, large and small counties, and each race and sex. The maximum misclassification occurs for Blacks (14.92% of officially recorded suicides). We conclude that suicides are misallocated to at least five other causes of death (two of which have not been previously considered in the literature) and are most likely to be underreported for groups with low official suicide rates, that is, Blacks and females. Consequently, Blacks and females are not as protected from suicide as was previously supposed. It may be inadvisable to use official suicide data to test scientific hypotheses about suicide, unless the effects of underreporting are estimated and, if necessary, corrected for.

Adult↗

PubMed1992

The microstructural tensile properties and biochemical composition of the bovine distal femoral growth plate.

The tensile properties of distal femoral growth plates from 12-month-old cows were determined on uniformly prepared straight bone-growth plate-bone specimens (7 x 7 mm2 in cross-section) from predetermined anatomical sites on the physis. Each specimen was distracted to failure using a computer-controlled servo-hydraulic testing machine at a strain rate of 0.004 s-1. It was found that the exponential constitutive law, using finite deformation formulation for strain, provides an excellent description of the stress-strain behavior of all the specimens up to the point of failure. The ultimate stress and both tangent moduli (i.e., the toe region tangent modulus and the tangent modulus calculated at 75% of ultimate strain) varied with anatomical site. The anterior region was the strongest, followed by the posterior/lateral. The anterior and posterior/lateral regions were also the stiffest, whereas the posterior/medial and center regions were the weakest and most compliant. The bone-growth plate-bone specimen exhibited a low ultimate strain (13.8% +/- 6%) that did not vary significantly throughout the growth plate. This result suggests that disruption of the physis may occur in vivo even at the lower distractions currently recommended for the clinical chondrodiatasis procedure for leg lengthening. The biochemical composition of the growth plate in the anatomical regions correlated well with the tensile properties. There was a greater collagen content in the regions that were the stiffest and strongest. The gross morphology of the growth plate of the bovine distal femur is also described in this study. There is a regular pattern to the undulations of the physis at several dimensional levels. Histologic findings showed that orientation of the hypertrophic cell columns and transphyseal septa are aligned nearly parallel to the longitudinal axis of the diaphyseal shaft. This column orientation is not affected by the undulation of the primary contour of the physis, which at certain locations may be inclined as much as 60 degrees relative to the diaphyseal axis. The orientation of the hypertrophic cell columns appears to be one of the dominant microstructural features influencing the tensile behavior of the bone-growth plate-bone specimens.

Animals↗

PubMed1991

Importance of the lay press in the transmission of medical knowledge to the scientific community.

BACKGROUND: Efficient, undistorted communication of the results of medical research is important to physicians, the scientific community, and the public. Information that first appears in the scientific literature is frequently retransmitted in the popular press. Does popular coverage of medical research in turn amplify the effects of that research on the scientific community? METHODS: To test the hypothesis that researchers are more likely to cite papers that have been publicized in the popular press, we compared the number of references in the Science Citation Index to articles in the New England Journal of Medicine that were covered by The New York Times with the number of references to similar articles that were not covered by the Times. We also performed the comparison during a three-month period when the Times was on strike but continued to prepare an "edition of record" that was not distributed; doing so enabled us to address the possibility that coverage in the Times was simply a marker of the most important articles, which would therefore be cited more frequently, even without coverage in the popular press. RESULTS: Articles in the Journal that were covered by the Times received a disproportionate number of scientific citations in each of the 10 years after the Journal articles appeared. The effect was strongest in the first year after publication, when Journal articles publicized by the Times received 72.8 percent more scientific citations than control articles. This effect was not present for articles published during the strike; articles covered by the Times during this period were no more likely to be cited than those not covered. CONCLUSIONS: Coverage of medical research in the popular press amplifies the transmission of medical information from the scientific literature to the research community.

Bibliographies as Topic↗

PubMed1991

Coding of interaural time differences of transients in auditory cortex of Rattus norvegicus: implications for the evolution of mammalian sound localization.

We obtained quantitative evidence on the coding of interaural time differences (ITDs) of click stimuli by 40 single neurons in the auditory cortex of anesthetized albino rats. Most of the neurons (31/40) received an excitatory input from the contralateral ear, and an inhibitory input from the ipsilateral ear (EI cells). These neurons expressed their sensitivity to ITDs in a sigmoidal relation between spike count and ITD, with maximal responses associated with contralateral-leading ITDs. The mean ITD dynamic range was 590 microseconds. The dynamic ranges typically encompassed at least part of the behaviorally-relevant range (about +/- 130 microseconds). Variations in ITD from 130 microseconds favoring one ear to 130 microseconds favoring the other ear caused spike response rate changes, on average, of 29.5%. These data are similar to those previously presented for the central auditory systems of larger mammals, whose auditory localization acuity is significantly better than that of the rat. We argue, therefore, that the sound localization mechanisms based on transient ITDs have not evolved in a fashion that covaries with interaural distance, and that there exists a mismatch between the ITDs the rat will encounter in the free field, and the ITDs which are encoded by its nervous system. This may be one reason why sound localization acuity has a roughly inverse relation to interaural distance.

Acoustic Stimulation↗

PubMed1991

Separate mechanisms control spike numbers and inter-spike intervals in transient responses of cat auditory cortex neurons.

In the anesthetized cat, some cortical auditory neurons discharge a train of up to 5 spikes in response to the onset of a characteristic frequency tone pulse. This report provides the first description of the inter-spike intervals (ISIs) in these responses. The ISIs were typically close to 2.0 ms in length, and, as indexed by the standard deviation of the interval length, were very regular. Except at threshold levels of stimulation, mean ISIs were relatively insensitive to both tone amplitude and repetition rate. This was true even over ranges of those variables that exerted dramatic effects on spike numbers and first spike latency. These data suggest that the relative timing of discharges within the spike burst is controlled by a mechanism which is separable from that which determines the number of spikes in them. The brevity of the ISIs suggest that they may be a means of enhancing the salience of the transient response against a background of spontaneous discharges.

Acoustic Stimulation↗

PubMed1991

Food caching in captive coyotes: stereotypy of action sequence and spatial distribution of cache sites.

This paper describes some aspects of the food caching behaviour of four captive coyotes. Detailed observations of the actions used by coyotes to cache food revealed them to be strikingly similar to those previously described for timber wolves. The similarities included the identity of the movements used, their temporal sequencing, and their susceptibility to interruption. This suggests that there exists a stereotypy across canids in the action sequences used in caching. Second, an examination of the distribution of cache sites revealed that each coyote scattered cache sites widely within a wooded region of their enclosure and preferentially in terrains close to exposed tree roots.

Animals↗

PubMed1990

Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex.

This paper explores the nature of the processing disorder which underlies the speech discrimination deficit in the syndrome of acquired word deafness following from pathology to the primary auditory cortex. A critical examination of the evidence on this disorder revealed the following. First, the most profound forms of the condition are expressed not only in an isolation of the cerebral linguistic processor from auditory input, but in a failure of even the perceptual elaboration of the relevant sounds. Second, in agreement with earlier studies, we conclude that the perceptual dimension disturbed in word deafness is a temporal one. We argue, however, that it is not a generalized disorder of auditory temporal processing, but one which is largely restricted to the processing of sounds with temporal content in the milliseconds to tens-of-milliseconds time frame. The perceptual elaboration of sounds with temporal content outside that range, in either direction, may survive the disorder. Third, we present neurophysiological evidence that the primary auditory cortex has a special role in the representation of auditory events in that time frame, but not in the representation of auditory events with temporal grains outside that range.

Animals↗

PubMed1990

Food-caching in timber wolves, and the question of rules of action syntax.

This report presents data on the sequence of motor operations used by captive timber wolves to cache food. Videotapes were obtained of 151 caching episodes by 8 wolves. The vast majority of these episodes contained 3 distinct phases, each composed of movements unique to that phase. The excavation of the cache site was always done with the forefeet, and burying of the food was always done with the snout. Both the identity of the movements, and the serial order of phases were independent of the sex of the animal, the season in which the observations were made, and the nature of the substrate. A comparison of the temporal sequencing of these actions with the temporal stereotypy seen in rodent motor patterns (e.g. grooming) revealed a striking phenomenological similarity. The factors shaping the temporal sequencing in the two behaviors are, however, probably very different. This is because much, though not all, of the temporal stereotypy in the sequence of movements used by the wolf in caching is constrained by the logistics of the cache operation, while this is not the case for the phases of facial grooming in rodents. The implications of our data for the kinds of behavioral evidence required for ascription of such stereotypy to a central pattern generator are discussed.

Animals↗

PubMed1990

Postponement of death until symbolically meaningful occasions.

This study shows that mortality dips before a symbolically meaningful occasion and peaks just afterward. Mortality among Chinese (n = 1288) dips by 35.1% in the week before the Harvest Moon Festival and peaks by the same amount (34.6%) in the week after. We chose to study mortality among Chinese and a Chinese holiday for two reasons. First, the holiday moves around the calendar, thus allowing separation of the effects of the holiday from fixed, monthly mortality effects. Second, the holiday appeals strongly to one (experimental) group and not to others (which can be used as control groups). In terms of percentage, cerebrovascular diseases displayed the largest dip/peak pattern, followed by diseases of the heart, and then malignant neoplasms. The dip/peak mortality pattern does not appear in various non-Chinese control groups. The statistical significance of the findings was demonstrated with linear and curvilinear regression analysis and with two nonparametric tests. After testing alternative explanations for the findings, we concluded that the dip/peak pattern occurs because death can be briefly postponed until after the occurrence of a significant occasion.

Aged↗

PubMed1990

Neural representation of sound amplitude in the auditory cortex: effects of noise masking.

Single auditory cortical neurons express their sensitivity to the amplitude of a preferred-frequency tone pulse as either a monotonic, saturating intensity profile or as a non-monotonic, bell-shaped intensity function. In the presence of continuous, wideband noise masking, the tone intensity profile is displaced toward higher tone levels. The magnitude of the tone threshold adjustments brought about by increments in noise level very closely match the elevations in noise amplitude. The mechanisms underlying the threshold adjustments likely include neural adaptation. This is because the tone threshold shifts seen in the spike count data are paralleled by spike latency data, and because recovery of tonal sensitivity following noise offset proceeds in a negatively-accelerating fashion. In some instances, the slope of the masked tone intensity profile is greater than that for unmasked tones. For masked tone levels evoking submaximal responses, this has the consequence that cortical responses to masked tones are somewhat more salient than those for unmasked tones of comparable suprathreshold level. These observations bolster our understanding of the psychophysics of noise-masking in normal listeners, and they provide a partial explanation of the difficulty shown by patients with temporal lobe lesions in discriminating signals in noise.

Animals↗

PubMed1990

Surgical treatment of scoliosis in a spinal muscular atrophy population.

Seventy-eight patients were diagnosed with spinal muscular atrophy between 1969 and 1988. Scoliosis developed in 34 of these patients, an incidence of 60%. Thirty-one patients could be retrospectively reviewed by chart review or interview. The average follow-up was 11.5 years. Onset of scoliosis averaged 8.8 years. Twenty-two patients were treated nonsurgically and nine surgically. Patients had improved sitting balance and endurance after surgery. Complications of surgery included loss of correction in one patient, one pseudarthrosis, and one patient who required prolonged ventilatory support. The prolonged survival of patients with spinal muscular atrophy justifies aggressive orthopaedic management of scoliosis to prevent progression of deformity and improve sitting comfort.

Braces↗

PubMed1990

Response timing constraints on the cortical representation of sound time structure.

The precision of spike response timing of 94 primary auditory cortex neurons was studied using conventional extracellular recording techniques in barbiturate-anesthetized cats to which tone- and/or noise-burst stimuli were presented using sealed sound delivery systems. Precision of spike timing was indexed using the standard deviation of the first-spike latent period in responses evoked by repeated presentation of tonal stimuli systematically varied in frequency, amplitude, and/or repetition rate. Within a neuron, variability of first-spike timing was usually proportional to the mean first-spike latency, in agreement with previous reports. In cases where there was a systematic relation between the precision of response timing and the mean latency, a linear correlation accounted for up to 90% of the data variance. Across the 94 neurons, standard deviations seen in responses of minimum latency were related to minimal mean latencies, and were typically in the range from 0.15-1.5 ms. The data suggest that responses to transients in the cortex show a precision of spike timing which is only slightly worse than that seen in cochlear-nerve fibers. This, however, is in dramatic contrast to previous evidence on the steady-state temporal response of cortical cells, which is at least an order of magnitude poorer than that seen in auditory-nerve fibers and many cochlear nucleus cells. These observations may be directly relevant to the known consequences of auditory cortex pathology in man.

Animals↗

PubMed1989

Timing of spike discharges in cat auditory cortex neurons: implications for encoding of stimulus periodicity.

Neurons at more central stations in the central auditory pathway show progressively poorer responses to high-frequency stimulus periodicities. This has been attributed to the relatively poorer spike timing in forebrain auditory neurons. This study directly examined the timing of spikes evoked by brief tone pulses which were varied in peak level and repetition rate. The experiments revealed that at tone repetition rates which produced progressively poorer entrainment, the timing of spike discharges remained sufficiently precise to support entrained responses. The fact that responses were poor indicates that imprecision in spike timing may not be the only factor limiting the encoding of temporal frequency. The data are discussed in relation to evidence on the temporal tuning of central neurons seen in studies using continuous amplitude modulations.

Acoustic Stimulation↗

PubMed1989

Coding of tone-pulse amplitude by single neurons in auditory cortex of albino rats (Rattus norvegicus).

We examined the neural representation of tone pulse amplitude in the auditory cortex of anesthetized albino rats. Rate-level functions for monaural, contralateral CF tones were obtained from single neurons. Most of these functions were saturating and monotonic in shape. The dynamic ranges of these functions were typically 5 to 35 dB in breadth, although the tail of this distribution extended to beyond 60 dB. The neurons with the widest dynamic ranges were usually those with the lowest CF thresholds. Nonmonotonic neurons were uncommon, and the nonmonotonicity was not as well developed as that seen in the cortex of cats and monkeys. For two individual rats, data are presented for neurons tuned to the same tone frequency in a single cerebral hemisphere. The CF thresholds of these neurons varied over a 50 dB range, and their collective dynamic ranges spanned at least 70 dB. These data provide a minimum estimate of the dynamic range of the cortical code for tone pulse amplitude in the rat. They suggest that there may be no serious mismatch between the neural and behavioral amplitude dynamic ranges.

Acoustic Stimulation↗

PubMed1989

Repetition rate and signal level effects on neuronal responses to brief tone pulses in cat auditory cortex.

This study describes the effects on the spike count, spike timing, and entrainment of cat auditory cortex neurons of parametric variations in the repetition rate and amplitude of a brief, characteristic frequency tone pulse. Data were obtained from single neurons in barbiturate-anesthetized cats to which signals were presented monaurally to the ear contralateral to the recording electrode. All neurons showed low-pass sensitivity to tone repetition rate. In cells with a monotonic rate response, the effect of an increasing stimulus level was to elevate the response rate and to extend performance to higher repetition rates. In nonmonotonic cells, cutoff frequencies (for repetition rate) varied with overall spike count. Latent periods increased with increases in repetition rate. This effect developed over the first few stimulus trials at any given repetition rate. Spike entrainment to the tone pulses varied with both repetition rate and signal level. Increases in signal level improved entrainment for responses to stimuli presented at low repetition rates, but entrainment at high repetition rates always saturated at significantly imperfect levels.

Acoustic Stimulation↗

PubMed1988

Death takes a holiday: mortality surrounding major social occasions.

To determine whether death can be postponed until after an important social occasion the number of deaths before and after the Jewish holiday of Passover (1966-84) were compared. Passover was chosen for study because it allows comparison of the participating and non-participating (control) groups, and it moves around the calendar (thus allowing separation of the effects of the holiday from the effects of the seasons). In the total Jewish sample (n = 1919), the number of deaths was lower than expected in the week before Passover and higher than expected in the week after (p = 0.045). This dip-peak pattern of mortality was concentrated among people with unambiguously Jewish surnames (p = 0.003) and did not appear in various control groups, including Blacks, Orientals, and Jewish infants. The pattern was most pronounced in the years when the holiday fell on a weekend, when it is most likely to be celebrated by the largest number of people (n = 183; p = 0.001). This pattern was statistically significant by binomial tests and by regression analyses of the data. The Passover pattern of mortality was found in each of the three leading causes of death.

Black or African American↗

PubMed1988

Primary auditory cortex in the ferret (Mustela putorius): neural response properties and topographic organization.

Microelectrode recording studies were made of the crown of the ectosylvian auditory cortex of barbiturate-anesthetized ferrets, using calibrated, sealed acoustic stimulus delivery systems. We confirmed our previous finding using free-field stimuli that this region of the ferret's cerebral cortex contains a tonotopically organized field in which neurons are briskly excited by the onset of tonal stimuli. The vast majority of neurons in this field were narrowly tuned to tone pulse frequency, with Q factors comparable to those described for cortical cells in other species. The distribution of minimum tone thresholds across the frequency representation of this field paralleled the behavioral audiogram in the same species. The majority of neurons received input from both ears, and the natures of the influences exerted by tonal stimuli at the two ears were similar in form to those described for other carnivores. The various binaural cell types had characteristic frequencies that spanned the entire tonal spectrum represented in the cortex. Preliminary mapping studies revealed that there may be a topographic segregation of cells according to their binaural interactions. The basic properties of cells in this region of the ferret's cerebrum are similar to those previously described for the cat's primary auditory cortex. The data on the binaural properties of these cells, and the spatial distribution of those cells, provide the first evidence in a species other than the cat for segregated binaural representation in the auditory cortex.

Acoustic Stimulation↗