Dennis McFadden

Relative lengths of fingers and toes in human males and females.

Digital scans of the hands and feet were obtained from 62 heterosexual females and 60 heterosexual males. Scans only of the hands were obtained from 29 homosexual females and 35 homosexual males. The lengths of the individual fingers and toes were estimated from those images by two experienced judges, and length ratios were constructed for all possible pairs of fingers (or toes) on each hand (or foot). Thumbs were not measured, but the great toe was measured and used to construct length ratios. Past research had concentrated on the relative lengths of the index and ring fingers (the 2D:4D ratio). This ratio is close to 1.0 in females and smaller than 1.0 in males. Here 2D:4D did exhibit the largest sex difference, for both hands, followed by 2D:5D and 3D:4D. The sex differences were larger for the right hand than for the left. For both homosexual females and homosexual males, nearly all of the length ratios for fingers were intermediate to those for heterosexual females and heterosexual males; that is, the ratios of homosexual females were masculinized and those of homosexual males were hypomasculinized, but few of these differences were significant. Because many toes were substantially arched, acceptable estimates of length often could not be obtained from the two-dimensional scans, meaning that conclusions about toes are much less certain than those for fingers. Nevertheless, the length ratios were generally larger for toes than for fingers, and the sex differences were generally smaller for toes.

Lateralization at high frequencies based on interaural time differences

Sensitivity to interaural time differences at high frequencies is demonstrated in a number of experiments. Two types of waveforms are used—bands of noise and two‐tone complexes. Variables studied are rate and depth of fluctuation of the envelope, overall intensity, and additivity of interaural time information across frequency regions. In many conditions of listening, sensitivity to interaural time differences at high frequencies compares favorably with sensitivity at low frequencies—good performace requires only tens of microseconds of interaural time delay.Subject Classification: [43]65.62, [43]65.68.

Aspirin abolishes spontaneous oto‐acoustic emissions

Spontaneous oto-acoustic emissions (OAEs) were measured prior to, during, and following administration of aspirin. The dose schedule was three 325-mg tablets every 6 h for a total of 16 doses (3.75 days). In every subject studied, all spontaneous OAEs gradually diminished and then disappeared during the drug regimen. Emissions that were initially small disappeared within 14-20 h of beginning the drug regimen (3-4 doses), while initially large emissions took 40-70 h (7-12 doses) to disappear completely. In contrast, the initial size of an emission appeared unrelated to the time required for it to recover to full strength once drug administration ceased. The recovery process was highly idiosyncratic, with the emissions of some subjects returning to full strength within 24 h, while for other subjects, full recovery required several days. In two subjects having multiple emissions in the same ear, the relative sizes of the different emissions often changed greatly during the disappearance and recovery phases. When small frequency shifts appeared for these subjects, they appeared--and were in the same direction--for each of the multiple emissions. In a related experiment, the spontaneous emission was unchanged in one subject who took a drug that inhibits the intracellular entry of calcium ions (verapamil).

Sex differences in the auditory system

A number of sex differences have been documented in the human auditory system. Females as a group have greater hearing sensitivity, greater susceptibility to noise exposure at high frequencies, shorter latencies in their auditory brain‐stem responses, more spontaneous otoacoustic emissions (SOAEs), and stronger click‐evoked otoacoustic emissions than males as a group. Males are better at sound localization, detecting binaural beats, and detecting signals in complex masking tasks than are females. During the first half of the menstrual cycle, several aspects of female hearing move in the male direction. The sex difference normally present in SOAEs is absent in females from opposite‐sex twin pairs. The implication is that their auditory systems have been masculinized prenatally by exposure to high levels of androgens produced by their male cotwins, analogous to an effect well established in other mammals. This suggests that some of the other sex differences in hearing are also attributable to differences in...

Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans

Otoacoustic emissions (OAEs) of two types--spontaneous and evoked distortion products--were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10-20 dB higher than when they were 100 Hz away from the SOAE frequency.

Aspirin-induced hearing loss as a model of sensorineural hearing loss

Performance in forward-masking, temporal-integration, and gap-detection tasks was measured in five normal-hearing subjects before and during a five-day period of aspirin use. The drug regimen was 3.9 g per day, taken in four equal doses at 6-h intervals. In the subjects showing substantial temporary hearing loss induced by the aspirin, (1) forward masking declined at about a normal rate as the masker-to-signal interval was increased, (2) the temporal-integration functions were flatter than normal, and (3) detection of a temporal gap was worse than normal at low sound-pressure levels (SPLs) but was essentially normal at levels above about 60 dB SPL. These aspirin-induced changes in performance are similar to the differences observed between normal listeners and listeners with mild sensorineural hearing loss. Thus, temporary, aspirin-induced hearing loss offers promise as a model condition for sensorineural hearing loss. The advantages offered by this model include all those typically attributed to within-subjects experimental designs, as well as the ability to manipulate the amount of hearing loss. Its primary disadvantages are that the hearing loss is not asymmetrically distributed toward the high-frequency region, as it typically is with sensorineural deafness, and there are large individual differences in the amount of temporary hearing loss induced by fixed doses of aspirin.

Masculinization Effects in the Auditory System

Otoacoustic emissions (OAEs) and auditory evoked potentials (AEPs) are different in several special populations of subjects. For females having opposite-sex co-twins (OSDZ females) and for homosexual and bisexual females, OAEs are masculinized. Certain AEP measures from homosexual and bisexual females also are masculinized. Certain AEP measures from homosexual males are hypermasculinized. These and other facts can be explained by assuming that these special populations received greater-than-normal exposures to androgens at some point(s) during development, possibly during prenatal development. It is proposed that some differences in androgenization may have been spatially and temporally localized rather than global, and that the localized response to androgen exposure sometimes may be nonmonotonic.

Comparison of Auditory Evoked Potentials in Heterosexual, Homosexual, and Bisexual Males and Females

The auditory evoked potentials (AEPs) elicited by click stimuli were measured in heterosexual, homosexual, and bisexual males and females having normal hearing sensitivity. Estimates of latency and/or amplitude were extracted for nine peaks having latencies of about 2–240 ms, which are presumed to correspond to populations of neurons located from the auditory nerve through auditory cortex. For five of the 19 measures obtained, the mean latency or amplitude for the 57 homosexual and bisexual females was different from that of the 49 heterosexual females in a manner that implies a masculinization of the auditory systems of the homosexual and bisexual females. A similar masculinization effect was previously observed for the otoacoustic emissions generated by the cochlea. For five other measures, the mean latency or amplitude for the 53 homosexual and bisexual males was different from that of the 50 heterosexual males in a manner that implies a hypermasculinization of the auditory systems of the homosexual and bisexual males. Hypermasculinization has been reported recently for other physical characteristics of homosexual males. One parsimonious interpretation of these findings is that homosexual males and females both were exposed to higher than normal levels of androgens at some point(s) in development. Data are reported only for the female subjects not using oral contraceptives because those drugs can masculinize certain AEP measures.

On the relation between hearing sensitivity and otoacoustic emissions

The auditory literature suggests that ears having spontaneous otoacoustic emissions (SOAEs) should also evidence overall better hearing in the quiet than ears with no SOAEs, but no direct tests of this presumed relationship have been made. Accordingly, hearing sensitivity was measured in both males and females having either no SOAEs or at least four SOAEs in the right ear. Averaged across frequencies, the hearing of the subjects with SOAEs was about 3 dB better, in both ears, than the hearing of the subjects with no SOAEs. In accord with past findings, sensitivity was also significantly better in right ears than left. However, the common finding of better hearing in females than males did not emerge, suggesting that this difference may exist only when the sex difference in SOAE prevalence is not taken into account. The existence of a direct relationship between hearing sensitivity in the quiet and the presence of SOAEs suggests that a common mechanism may be responsible for both.

Masking-level differences determined with and without interaural disparities in masker intensity.

Psychometric functions were obtained for three listeners for the interaural conditions Nm‐Sm and N0‐Sπ using seven different noise spectrum levels. In addition, data were collected on the N0‐Sπ condition with the spectrum level in one ear smaller than that in the other ear. In these N0′‐Sπ′ conditions, the signal‐to‐noise ratio was kept equal in the two ears. The masking‐level differences (MLDs) for the N0‐Sπ conditions declined gradually as the level of the noise was reduced, and for small spectrum levels, they were essentially the same as the MLD obtained when the masker was turned off. The MLDs declined more rapidly for the N0′‐Sπ′ conditions, but a small MLD was obtained even when the spectrum level in one ear was 60 dB smaller than that in the other ear. For the Nm‐Sm conditions, masking increased linearly with increases in spectrum level, but for N0‐Sπ, the relation was not linear—a further indication that the basis for detection is different in MLD and non‐MLD conditions. The results are discusse...