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PubMed1984

The detection of motion in the peripheral visual field.

To assess the sensitivity of the periphery to motion, we measured differential motion detection and velocity discrimination as a function of eccentricity in the lower visual field. The differential motion threshold, a measure of the ability to detect relative motion (shear) between adjacent visual stimuli, is smaller than the minimum angle of resolution at all retinal loci tested. The target size required to produce the lowest differential motion threshold is surprisingly large, ranging from 1 deg in the fovea to about 20 deg at 40 degrees eccentricity. When the peripheral thresholds for differential motion and for resolution are normalized against the fovea and plotted on linear axes, the eccentricity functions are linear. Velocity discrimination (delta V/V) is as precise in the periphery as it is in the fovea, amounting to about 6% for the optimum velocity range. In the fovea, the minimum Weber fraction is reached at velocities of 5 deg/sec or faster. In the periphery this minimum is found for a faster range of velocities (greater than 30 deg/sec at 40 degrees eccentricity). If target velocity is expressed in the resolution units/second appropriate to each tested eccentricity, the velocity discrimination functions coincide. Thus, while the spatial determinants of velocity discrimination follow the change in resolution found with eccentricity, peripheral temporal sensitivity must be nearly equal to foveal temporal sensitivity.

Fovea Centralis↗
PubMed2002

Dorsal gradient networks in the Drosophila embryo.

Here, we describe one of the major maternal regulatory gradients, Dorsal, and threshold outputs of gene expression that result from the graded distribution of this transcription factor. The analysis of a large number of authentic and synthetic target genes suggests that the Dorsal gradient directly specifies at least four, and possibly as many as seven, different thresholds of gene activity and tissue differentiation. These thresholds initiate the differentiation of the three primary embryonic tissues: the mesoderm, neurogenic ectoderm, and dorsal ectoderm. Moreover, primary readouts of the Dorsal gradient create asymmetries that subdivide each tissue into multiple cell types during gastrulation. Dorsal patterning thresholds represent the culmination of one of the most complete gene regulation network known in development, which begins with the asymmetric positioning of the oocyte nucleus within the egg chamber and leads to the localized activation of the Toll-Dorsal signaling pathway in ventral regions of the early embryo.

Animals↗
PubMed1993

Magnification perimetry.

PURPOSE: The authors used a method of spatial scaling to quantify the eccentricity-related decline in differential light sensitivity as a function of visual field meridian and age. METHODS: Differential light threshold at the fovea was measured in two groups of subjects of differing age (young mean age, 23.6 yr; standard deviation, 2.4 yr; elderly mean age, 69.6 yr; standard deviation, 6.2 yr) using a Goldmann size I stimulus moving across fixation at 1 degree/sec. With luminance kept constant, eccentricity thresholds for kinetic stimuli of increasing magnification were then measured. The results were analyzed in terms of the E2 value, which specifies the eccentricity at which the stimulus size must double to maintain performance equivalent to that at the fovea. RESULTS: For the young subjects, eccentricity thresholds increased linearly with an increase in stimulus diameter for most meridians. E2 varied between 5-12 degrees, depending on the meridian, and showed the same meridional trend as that of retinal ganglion cell distribution, although the magnitudes of E2 were different. For the elderly subjects, the eccentricity thresholds increased in a nonlinear manner with the stimulus diameter. CONCLUSIONS: Further factors, such as spatial summation, must also determine the eccentricity dependence of the differential light threshold because ganglion cell density decreases at a much faster rate than the differential light threshold. The most marked effects of age on differential light sensitivity occur at the fovea and beyond 20 degrees in the peripheral field, with a relative sparing in the pericentral area.

Adult↗
PubMed1979

Spatial firing patterns of auditory neuron network modelling by computer simulation.

This communication examines, in digital computer simulated network, input signals and response patterns established at excitatory neurons' level i.e. the membrane potential of neuron soma. It is restricted to spatial patterns of the auditory neuron networks and time factor for nervous conduction and transmission is neglected compared with long maintained membrane potentials of neuron somas. The model analyzes the change in the spatial patterns of the membrane potential in the two dimensional networks of the auditory system. In order to evaluate the contribution of the various parameters, it is started that the simplest model has only one parameter, lateral inhibition. The other parameters are then added, one at a time, to successive models. The lateral inhibition is a necessary condition in the auditory nervous system if any sharpening of the response areas in the single neurons is to occur. A necessary condition for the validity of the model is that is should be applicable to the other senses such as vision and chemical patterns, taste. The threshold feature of auditory neurons aids in producing a sharpening in the neuron of the auditory relay nuclei. It does this clipping the spatial response patterns in one dimensional arrays of excitatory neurons. Recurrent inhibition seems a necessary condition in the sensory nervous system that any kinds of input signals are to be preserved over a wide range of stimulus intensity. In other words, this network has a wide dynamic range against any kinds of input signals. A simple self-recurrent negative feedback does not contribute to the sharpening, but more complex socalled averaged type does. A neuron network is capable of responding stably to stimuli with a wide range of intensity and with any kind of spatial patterns if there is a simple negative feedback mechanism. When there is no negative feedback, input signals soon disappear or saturate in the neuron network. Therefore, recurrent inhibition is the most important mechanism. Spontaneous activity appears to aid in the sharpening by providing a kind of contrast, that is by reducting the amount of activity in neurons adjacent to the excitatory area. Moreover, the effect of spontaneous activity in the model seems to make repples around the excitatory area and suggests that an introduction of activity at any stage of the networks, from whatever source for example reticulum formation and thalamus, might appreciably alter the response patterns at subsequent neuron network. This suggests that the mechanism of the consciousness that might be controlled by the thalamus and or reticular formation. These two dimensional neuron networks may be expanded to three dimensional neuron networks. The former might simulate the auditory nervous system while the latter might simulate the visual system.

Animals↗
PubMed2002

Relationship of exercise test variables to cycling performance in an Ironman triathlon.

The purpose of this study was, firstly, to investigate the intensity of exercise performance of highly trained ultra-endurance triathletes during the cycling portion of an Ironman triathlon, and, secondly, to examine the anaerobic threshold and its relationship to this performance. Following a peak oxygen consumption (VO(2peak)) test on a cycle ergometer to determine the heart rate (HR(Th,vent)) and power output (PO(Th,vent)) at the ventilatory threshold (Th(vent)), 11 highly trained male triathletes [mean (SEM) age 35.8 (1.6) years, body fat 11.7 (1.2)%. VO(2peak) 67.5 (1.0) ml x kg(-1) x min(-1)] who were participating in an Ironman triathlon, in random order: (1) cycled at their PO(Th,vent) (Bi(Th,vent)) until they were exhausted, and (2) cycled for 5 h at a self-selected intensity (Bi(SSI)). Cycling power output (PO), oxygen uptake (VO(2)), heart rate (HR) and blood lactate concentration ([La(-)](b)) were recorded at regular intervals during these trials, while performance HR was recorded during the cycling phase of the Ironman triathlon. Significantly greater (P < 0.05) values were attained during Bi(Th,vent) than during Bi(SSI) for PO [274 (9) compared to 188 (9) W], VO(2) [3.61 (0.15) compared to 2.64 (0.09) l x min(-1)], and [La(-)](b) [6.7 (0.8) compared to 2.8 (0.4) mmol x l(-1)]. Moreover, mean HR during the Ironman triathlon cycle phase [146.3 (2.4) beats.min(-1); n=7] was significantly greater than mean HR during Bi(SSI) [130 (4) beats x min(-1)], and significantly less than mean HR during Bi(Th,vent) [159 (3) beats x min(-1); all P < 0.05]. However, HR during the cycle portion of the Ironman triathlon was highly related to (r = 0.873; P < 0.05) and not significantly different to HR(Th,vent) [150 (4) beats x min(-1)]. These data suggest that ultra-endurance triathletes cycle during the Ironman triathlon at a HR intensity that approximates to HR(Th,vent), but at a PO that is significantly below PO(Th,vent).

Adult↗
PubMed2006

Critical velocity during continuous and intermittent exercises in children.

The purpose of this study was to apply the "critical velocity" concept to short intermittent high-intensity running exercises in prepubescent girls and boys and to compare the running performances obtained either by intermittent or continuous exercise runs. Eleven 8 to 11-year-old children underwent a maximal graded field test to determine peak oxygen uptake (peakVO2) and maximal aerobic velocity (MAV). During the six following sessions, they randomly performed three continuous runs (90, 100, and 110% of MAV) and three intermittent runs (120, 130, and 140% of MAV) until exhaustion. Intermittent exercises consisted of repeated 15 s runs each one separated by a 15 s passive recovery interval. For continuous as well as intermittent exercises, distance versus time to exhaustion (TTE) relationships were calculated to determine continuous (CVc) and intermittent (CVi) critical velocities. Values for peakVO2 and MAV were 45.8 +/- 5.3 ml x kg(-1) x min(-1) and 10.5 +/- 1.0 km h(-1), respectively. For the whole population, a significant relationship was found between the distance to exhaustion (DTE) and TTE for continuous (r2= 0.99, P < 0.05) and intermittent exercises (r2 = 0.99, P < 0.05). Significant relationships were found between peakVO2 and both CVc (r2= 0.60, P < 0.01) and CVi (r2= 0.47, P < 0.05). In conclusion, as for continuous exercises, a linear relationship was found between DTE and TTE for short high-intensity intermittent exercises. CVc was significantly related to peakVO2, while a significant lower relationship was found between peakVO2 and CVi.

Anaerobic Threshold↗
PubMed2006

Dead regions in the cochlea and enhancement of frequency discrimination: Effects of audiogram slope, unilateral versus bilateral loss, and hearing-aid use.

Following a restricted lesion of the cochlea, which produces a "dead region" (DR), animal experiments have revealed an increase in the cortical representation of frequencies just below the edge frequency (f(e)) of the DR. This may result in improved difference limens for frequency (DLFs) just below f(e). In previous studies to assess this, the value of f(e) was not determined precisely. We measured DLFs using human subjects with DRs for whom the values of f(e) had been determined precisely using psychophysical tuning curves. To prevent use of loudness cues, stimuli for the measurement of DLFs had a mean level falling along an equal-loudness contour and levels were roved over a 12-dB range. DLFs were measured for thirteen subjects with a DR in at least one ear. Almost all subjects with bilateral hearing loss exhibited enhanced DLFs near f(e), consistent with cortical reorganisation. This occurred for subjects whose audiograms had both steep and shallow slopes, regardless of hearing aid use, and for two subjects with low-frequency DRs. One subject with a high-frequency DR in one ear and good hearing in the other ear showed an enhanced DLF in her better ear.

Acoustic Stimulation↗
PubMed2006

Age-related differences in identification and discrimination of temporal cues in speech segments.

This study investigated age-related differences in sensitivity to temporal cues in modified natural speech sounds. Listeners included young noise-masked subjects, elderly normal-hearing subjects, and elderly hearing-impaired subjects. Four speech continua were presented to listeners, with stimuli from each continuum varying in a single temporal dimension. The acoustic cues varied in separate continua were voice-onset time, vowel duration, silence duration, and transition duration. In separate conditions, the listeners identified the word stimuli, discriminated two stimuli in a same-different paradigm, and discriminated two stimuli in a 3-interval, 2-alternative forced-choice procedure. Results showed age-related differences in the identification function crossover points for the continua that varied in silence duration and transition duration. All listeners demonstrated shorter difference limens (DLs) for the three-interval paradigm than the two-interval paradigm, with older hearing-impaired listeners showing larger DLs than the other listener groups for the silence duration cue. The findings support the general hypothesis that aging can influence the processing of specific temporal cues that are related to consonant manner distinctions.

Adolescent↗
PubMed1998

The role of the chinchilla pinna and ear canal in electrophysiological measures of hearing thresholds.

Measurements of the acoustic transfer function (ATF) of the pinnae of 8 chinchillas were compared with the auditory-evoked potential (AEP) thresholds of 16 chinchillas measured in free field and with insert earphones. The ATF was measured in anesthetized chinchillas in a far-field condition in a semi-anechoic room using a logarithmic frequency sweep from 100 Hz to 20 kHz. Probe microphone measurements were collected with the probe opening at the tympanic membrane and in the same approximate position with the chinchilla removed from the sound field. For each animal's acoustic transfer function, the average of five in-the-ear and three free-field measurements were determined. The ATF exhibited a 5-dB passive gain at about 1 kHz and a broad resonance between 2.5 and 6 kHz of about a 10-dB gain. AEP thresholds were obtained from monaural chronically implanted chinchillas at 0.5, 1, 2, 4, and 8 kHz using first free-field and then insert earphone stimuli. The free-field sound pressure was measured with a microphone in the approximate position of the chinchilla's head. The earphone sound pressures were measured with a probe microphone positioned near the tympanic membrane. The free-field AEP hearing thresholds exhibited +10-dB gain at 4 kHz compared to the insert earphone AEP thresholds. The agreement between the ATF and AEP derived transfer function suggested that the threshold differences at 4 kHz between the two testing configurations can be accounted for by the pinna and ear canal gain.

Acoustic Stimulation↗
PubMed1998

The level and growth behavior of the 2 f1-f2 distortion product otoacoustic emission and its relationship to auditory sensitivity in normal hearing and cochlear hearing loss.

The 2 f1-f2 distortion product otoacoustic emission (DP) was measured in 20 normal hearing subjects and 15 patients with moderate cochlear hearing loss and compared to the pure-tone hearing threshold, measured with the same probe system at the f2 frequencies. DPs were elicited over a wide primary tone level range between L2 = 20 and 65 dB SPL. With decreasing L2, the L1-L2 primary tone level difference was continuously increased according to L1 = 0.4L2 + 39 dB, to account for differences of the primary tone responses at the f2 place. Above 1.5 kHz, DPs were measurable with that paradigm on average within 10 dB of the average hearing threshold in both subject groups. The growth of the DP was compressive in normal hearing subjects, with strong saturation at moderate primary tone levels. In cases of cochlear impairment, reductions of the DP level were greatest at lowest, but smallest at highest stimulus levels, such that the growth of the DP became linearized. The correlation of the DP level to the hearing threshold was found to depend on the stimulus level. Maximal correlations were found in impaired ears at moderate primary tone levels around L2 = 45 dB SPL, but at lowest stimulus levels in normal hearing (L2 = 25 dB SPL). At these levels, 17/20 impaired ears and 14/15 normally hearing ears showed statistically significant correlations. It is concluded that for a clinical application and prediction of the hearing threshold, DPs should be measured not only at high, but also at lower primary tone levels.

Adolescent↗
PubMed1988

Binaural hearing after middle ear surgery. Masking-level difference for interaural time and amplitude cues.

Previous investigations have shown that binaural hearing is often abnormal in patients having conductive hearing losses, and even in patients who have had hearing thresholds corrected by middle ear surgery. The present study assessed further the masking-level difference (MLD) in patients who had previously undergone middle ear surgery. The stimuli were chosen such that the sensitivity to interaural time difference cues and to interaural amplitude difference cues could be assessed independently. Results indicated that the MLD is abnormal in more than a third of 15 patients, even after surgery has restored normal hearing at the frequency of the test. The MLD is more likely to be reduced for the cue of interaural time difference than for interaural amplitude difference. Subjects who had lesions of long duration, early onset, and large asymmetry were particularly likely to have reduced MLDs.

Adolescent↗
PubMed1990

Evoked-response tone-on-tone masking in the chinchilla: effect of masker frequency.

Tone-on-tone masking patterns were measured at 0.5, 1, and 4 kHz using the auditory-evoked response from the inferior colliculus of the chinchilla. Masking profiles obtained with a masking level of 30 dB SPL were relatively symmetrical; however, as masker level increased, masking spread toward the high frequencies, particularly with the 0.5-kHz masker. For masker frequencies of 1 and 4 kHz, a low-threshold notch was observed in the masking profile 2/3 of an octave above the frequency of the masker. The low-threshold notch may represent a response to the distortion tone 2F1-F2. The notch was absent in the 0.5-kHz masking profile. The masking profiles obtained with the evoked response are somewhat wider, but otherwise qualitatively similar to those measured psychophysically in humans. Thus, the evoked-response procedure may provide a convenient way of evaluating the spread of masking and the presence of distortion tones in difficult-to-test subjects.

Acoustic Stimulation↗
PubMed1991

Frequency resolution after successful surgery in congenital ear anomalies.

Frequency resolution was studied in patients with a unilateral congenital ear defect (atresia), who were successfully operated on. Psychophysical tuning curve (PTCs) were obtained. A comparison of the shapes of the PTCs revealed that the average curve for all the patients was much alike for the operated and non-operated (normal) ear: broad tuning curves, as reported from animal studies, were not found. After appropriate corrections were made for the small remaining air-bone gaps, as seen in all patients, the PTCs of all the operated ears lay reasonably well within the 2 S.D. range of the average PTC obtained in subjects with normal hearing.

Adolescent↗
PubMedDate not supplied

Psychoacoustic evaluation of present prostheses.

A battery of psychoacoustic tests, designed to specify auditory discriminations possible with present, single-channel auditory prostheses, was administered successfully to 12 of the 13 subjects. While no subject was able to perform all discriminations required by this battery of tests, there was no discrimination that at least one subject did not perform successfully. The typical subject could 1) discriminate intensity differences within normal limits for frequencies below 1000 Hz; 2) discriminate frequency differences quite normally at 125 and 250 Hz, but not at all at 1000 or 2000 Hz; 3) discriminate differences in signal duration, temporal patterning (rhythm), and spectrum (e.g., tone vs narrow-band noise); and 4) discriminate between pairs of synthesized vowel-like sounds. The results of masking experiments could only be interpreted in terms of intensity discrimination. Several subjects were able to relate stimulus intensity to loudness for low-frequency sounds; and they could relate stimulus frequency to pitch for signals below 25 Hz. The intelligibility of the subjects' speech was found to improve when their prostheses were activated.

Auditory Threshold↗