Edward A. Cudahy

Qualitative analysis of scopolamine-induced amnesia.

The neurochemistry of memory remains to be determined. Acetylcholine may be one of the neuotransmitters which mediates memory function, since the anticholinergic drug scopolamine produces amnesia in man. This study of scopolamine-induced memory deficits further defines those cognitive processes which are disrupted. The drug does not diminish attention, as assessed with an auditory vigilance task, or initial signal detection. More complex auditory decoding is affected, however. Scopolamine impairs aspects of initial memory acquisition (e. g., encoding and consolidation) and spontaneous memory retrieval. Retention is unaffected. Precise delineation of the neurochemistry of human memory will require comparative studies of amnesia-producing compounds, systematically examining the neuropsychological processes impaired by each.

Human underwater and bone conduction hearing in the sonic and ultrasonic range.

Several investigators have reported that high‐intensity bone‐conducted sounds in the ultrasonic range (>20 kHz) can produce auditory sensations in individuals with normal hearing. Underwater hearing threshold studies performed at the Naval Submarine Medical Research Laboratory have found audibility curves similar to those previously reported in bone conduction studies. Human underwater and bone conduction behavioral thresholds in the frequency range between 20 Hz and 200 kHz are presented. Accelerometry measurements made with a mechanical human‐head simulator are also presented. The present findings support the argument that the primary mechanism for human underwater hearing is bone conduction. Possible mechanisms for the underwater ultrahigh frequency hearing will be discussed.

Low‐frequency response of the submerged human lung

A study was undertaken to determine the response of the human lung to low‐frequency underwater sound in the range of 20 to 500 Hz. Experiments were conducted in a 1100 gal tank inside a hyperbaric chamber. Lung responses were measured by three independent techniques: a hydrophone close to the chest, an accelerometer attached to the chest, and a noninvasive ultrasound measurement of the lung surface. Ten subjects were tested. Each subject was tested twice at ambient pressures of 0, 10, 60, and 120 ft of sea water (FSW). The dominant feature of the response was a strong resonance that occurred, on average, at 39 Hz at surface pressure and 71 Hz at a depth of 120 FSW. This appears to be the fundamental resonance of the lungs. The depth dependence indicates that lung stiffness is dominated by gas in the lungs with a small contribution from the chest wall. Resonance Q’s were in the range of 5 to 7. There is evidence in the data of other low‐frequency resonances that can be attributed to intestinal gas. Other than these, the lung acceleration response to incident pressure above resonance appears to be flat. [Work supported by ONR.]

Developmental, age, and sex effects on gap detection and temporal order

Developmental effects on gap detection and temporal order performance were examined cross sectionally in 18 males between 6 and 17 years, while age effects in adults were examined cross sectionally in 38 males and 23 females between 18 and 70 years of age. Thresholds for gap detection and temporal order were measured using a 21FC procedure. The gap was embedded in broadband noise while the signals for the temporal order task were 1000‐ and 2500‐Hz tones. Percent correct detection and reaction time were assesed during a 15 min go‐no‐go vigilance task with a tonal signal at 10‐dB sensation level in white noise. There was a statistically significant correlation between the young boys ages and temporal order threshold. Gap detection and temporal order thresholds were significantly correlated with age for the adult males but the relation was most marked after age 50. Significant correlations were found between age and all measures for the females. In addition to main effects for sex and age, there was a significant sex by age interaction for gap detection.

Temporal tuning curves and their relation to frequency tuning curves

Temporal tuning curves for a 1000‐Hz, 10‐ms, 10‐dB SL sinusoidal signal with a 500‐, 1000‐, or 1500‐Hz, 10‐ms sinusoidal masker were measured using a 2IFC adaptive procedure. Frequency tuning curves for the 10 dB SL, 1000‐Hz signal were also measured for 10‐ and 500‐ms simultaneous maskers. Five normal hearing listeners were employed. The frequency tuning curves for the brief masker were broader than those for the long masker, especially on the high‐frequency side of the signal. Marked differences were not found between the temporal tuning curves for the three masker conditions. The implications of these results for relations between auditory frequency and temporal analysis will be discussed.

A re‐examination of human underwater sound localization abilities in the azimuth.

Divers are frequently exposed to underwater sounds. The subjective impression of the diving community is that sound localization underwater is extremely difficult. However, Feinstein [1973a, 1973b] found underwater minimum audible angles (MAAs) to be approximately 10 deg. To the extent that underwater MAAs reflect the general performance of the binaural system, this would suggest that humans should be reasonably effective at underwater sound localization. A re‐examination of the underwater MAAs, with greater subject and environment control, was performed. The present work indicates underwater MAAs at approximately 20–30 deg, significantly poorer than previous findings. [Work supported by the ONR.]

Underwater loudness for pure tones: Duration effects

The loudness of underwater pure tones was measured by loudness matching for pure tones from 100 to 16,000 Hz. The standard was a one second tone at 1000 Hz. The signal duration was varied from 20 milliseconds to 5 seconds. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. Loudness was measured at the threshold, the most comfortable loudness, and the maximum tolerable loudness. The intensity of the standard was varied randomly across the test series. The subjects were bareheaded U.S. Navy divers tested at a depth of 3 meters. All subjects had normal in‐air hearing. Tones were presented to the right side of the subject from an array of underwater sound projectors. The sound pressure level was calibrated at the location of the subject’s head with the subject absent. Loudness increased and threshold decreased as duration increased. The effect was greatest at the lowest and highest frequencies. The shape of the loudness co...

Loudness for tone underwater

The loudness for pure tones was measured by loudness matching for 1‐s pure tones from 100 to 50 000 Hz. The standard tone was 1000 Hz. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. The standard was presented at one of five sound pressure levels (SPL) for each set of frequencies. The standard SPL was varied randomly across test series. The subjects were bareheaded US Navy divers tested at a depth of 3 m. All subjects had normal hearing. The tones were presented to the right side of the subject from an array of underwater sound projectors. The SPL was calibrated at the location of the subject’s head with the subject absent. The loudness increased more rapidly as a function of standard SPL at mid‐frequencies than at either high or low frequencies. The most compact loudness contours (least SPL change across range of standard SPL) were at 50 000 Hz. The underwater loudness contours across frequency are significan...

Underwater loudness for tones

The loudness for pure tones was measured by loudness matching for 1‐s pure tones from 100 to 50 000 Hz. The standard tone was 1000 Hz. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. The standard was presented at one of five sound pressure levels (SPL) for each set of frequencies. The SPL was varied randomly across a test series. The subjects were bareheaded U.S. Navy divers tested at a depth of 3 m. All subjects had normal hearing. The tones were presented to the right side of the subject from an array of underwater sound projectors. The SPL was calibrated at the location of the subject’s head with the subject absent. The loudness increased more rapidly as a function of standard SPL at mid‐frequencies than at either high or low frequencies. The most compact loudness contours (the least SPL change across the range of standard SPL) were at the highest frequency. Loudness contours across frequency derived from thes...

Critical band distortion analysis: Part II

Distortion analysis typically focuses on the physical measurement of distortion. There is little information on the relation between these measurements and perception. A series of studies has been conducted as part of the development of a general method for measuring distortion, based on a simple critical band model of hearing, that links physical measurement with the perception of distortion. Results from both detection and ranking experiments using paired comparison measures of speech processed through a hearing aid will be reported. These results suggest that a critical band analysis of distortion can be useful for relating physical and perceptual measures of distortion, at least for simple stimuli. The limitations of the measure will also be discussed. [Research supported by NIDRR.]