Relative Difference Limens Research Articles

Frequency discrimination by infants and adults

Frequency difference thresholds were estimated for infants (5 to 8 months old) using the visually reinforced head‐turn procedure. Stimuli were 500‐ms tone bursts at six frequencies ranging from 250 to 8000 Hz presented monaurally via a TDH‐49 earphone. Tone bursts were presented at 70 dB above adult absolute threshold. An adaptive threshold estimation procedure with a variable step size was used. An adult group was run using the same protocol. The relative difference threshold (Δf/f) was a nonmonotonic function of frequency with a minimum around 1000 Hz for both age groups. However, infants had higher thresholds than adults at frequencies from 250 to 2000 Hz (approximately 2% for infants versus 1% for adults). No age difference in threshold was observed at 4000 or 8000 Hz. Age differences in absolute sensitivity at low frequencies [Trehub et al., J. Exp. Child Psychol. 21, 219–225] are not great enough to account for the rather large difference in discrimination performance in the low‐frequency range. It is suggested that these findings reflect continuing development of the analytic capacity of the auditory system during the first year of life. [Work supported by Virginia Commonwealth University Faculty Grants‐in‐Aid.]

Psychophysical studies for two multiple-channel cochlear implant patients.

Psychophysical studies were conducted on two multiple-channel cochlear implant patients to examine the nature of the hearing sensations produced by electrical stimulation of auditory nerve fibers using electrodes at different sites in the scala tympani (one electrode at a time). Both time-invariant stimuli, whose parameter values did not vary in time, and time-varying stimuli, specified by a linear variation in parameter values, were used. A sharpness ranking study using time-invariant signals suggested that the hearing sensations produced by different electrodes varied from dull to sharp in an apical to basal direction in the scala tympani. A categorization study showed that the hearing sensations produced by two adjacent electrodes (1.5 mm apart) were rarely confused for a restricted range of time-invariant pulse rates. Discriminability studies by a same-different procedure for stimuli with pulse rate below 250 pps showed: (1) relative difference limens of 6% to 12% for time-invariant pulse rates, and 9% and 13% for time-varying pulse rates; (2) stimuli with time-varying electrode position differing in the direction of electrode trajectory were readily discriminated; and (3) the discrimination of time-varying pulse rates deteriorated with decreases in the duration of the variation, while the discriminability of single-electrode trajectories was the same for the three durations: 25, 50, and 100 ms. A speech processing strategy was also proposed on the bases of these results.

Discrimination of the intensities of tones by the parakeet (Melopsittacus undulatus)

Using avoidance conditioning and a modified method of limits, we measured the intensity difference limens of three parakeets at six sensation levels of a 2.86-kHz tone. At sensation levels above 50 dB, the average value of the relative difference limen is about 3.0 dB. Below a sensation level of 50 dB, the relative difference limen increases as the intensity of the tone is decreased. Intensity difference limens for the parakeet are 2–3 dB larger than similar measures for man and other mammals and suggest that the avian ear may not be as sensitive to intensity changes as are the ears of many mammals. [Supported by NIH Grant No. NS 03856 to the Central Institute for the Deaf.]

Auditory Frequency Discrimination in the Atlantic Bottlenose Dolphin, Tursiops truncatus Montague: A Preliminary Report

Data taken on one Tursiops truncatus are presented for relative difference limens (DLs) in acoustic frequency discrimination. Base frequencies range from 0.9 to 90.0 kHz. The most sensitive frequency discrimination lies in a band between 2.0 and 20.0 kHz. Weber ratios range in value from 0.0028 to 0.0121.

Differential Sensitivity for Duration

Differential sensitivity to acoustic signal duration was determined for a group of normal-hearing, well-practiced listeners. A modified psychophysical method of limits was employed to obtain a difference limen for each of 18 combinations of stimulus frequency (250, 1000, and 4000 cps), sensation level (10 and 50 dB), and reference duration (300, 500, and 1000 msec). Treated as a randomized complete block 2×3×3 factorial design and submitted to an analysis of variance, the data permit the following conclusions: (1) the magnitude of the relative difference limen is considerably smaller than has been reported previously; (2) the magnitude of the relative difference limen of pure-tone auditory stimuli is related to duration of the reference stimulus and to sensation level; (3) the magnitude of the relative difference limen of duration is not highly dependent on stimulus frequency; (4) relative to duration judgments, Weber's law appears to be valid only in the case of midrange and relatively high stimulus frequencies and at a moderately high sensation level.

ASTUDY OF THE PURE-TONE DISCRIMINATION IN DEAFMUTE

Seventy eight cases of deafmute children (congenital deafmutes 43, acquired deafmutes 35 from the school for the deafmute associated with Tokyo University of Education) were investigated concerning loudness discrimination (differencelimen of loudness), threshold of pain and auditory area of pure tones at the frequencies of 4, 000, 1, 000 and 250cps. Results obtained were as follows:(1) The mean values of DL at 50% correct judgment at were found to be between 0.9dB and 1.2dB, and those of DL at 80% correct judgment were between 2.1dB and 2.8dB.(2) Difference limen of loudness measured at the intensity of "not too loud" and "not too low" showed significant difference at 4, 000 and 1, 000 cps between the congenital and acquired deafmutes.(3) Comparison of the DL with the normal DL measured at 40dB above the threshold of hearing was made and there was no significant difference between the congenital deafmute and the normal, but significant difference between the acquired deafmute and the normal.(4) Thresholds of pain were distributed between the threshold of pain and uncomfortable loudness level of the normal, and the auditory area of deafmutes became remarkably narrow.Part II. Pitch Discrimination and Equal Loudness Curves of DeafmuteSixty three cases of deafmutes (congential 33, acquired 27 from the school for the deafmute associated with Tokyo University of Education and female adults of acquired deafmutes 3) were studied on pitch discrimination (DL on pitch) and equal loudness curves (ELC).Results were obtained as follows:(1) It was found the DL on pitch (relative difference limen measured on ELC at 4, 000, 2, 000, 1, 000, 500 and 250cps) was distributed in wide range and showed the mean values of 10-20% which were much larger than the normal values.(2) It should be generally considered that ELC was separated widely from the auditory threshold curve in the lower frequencies, but slightly deviated from a parallel relationship with the threslhod curve in the higher frequencies. The ELC in the lower frequencies showed the opposite inclination to normal ELC. It was concluded that the changes in loudness sensation to the intensity of sound were more abrupt in higher frequencies than in lower frequencies.

Visual sensitivity to the rate of electrically produced intermittence.

Temporal resolution of the neural and cortical components of vision was studied with periodic electric stimuli as a means of by-passing the photochemical retina. Difference-limens for discriminating the frequency of the faint flashes of light due to the passage of current through the eye were obtained at 13 frequencies between 5 and 45 cps. The wave form of the periodic current was square with no dc component, and the current level was set by a method developed to produce electrical phosphenes of the same intensity at each frequency. Data from two observers give average deviations (ΔF) from the standard frequency (F) of 0.11 to 0.62 cps. The relative difference-limens, ΔF/F, lie between 0.009 and 0.03. Graphic integration of 1/ΔF gives 127 just noticeable differences in the range studied. The graph relating ΔF and F shows ΔF to be a complex function of F. Recent data on the discrimination of photic intermittence also show ΔF to be a complex function of F, although of a quite different form in the frequency range between 15 and 40 cps. These results with square waves of current are compared with earlier work on the differential sensitivity of the eye to the frequency of sine waves.

Difference-Limens for Photic Intermittence

Difference-limens for visual intermittence were measured in the range of one to 45 cps. The standard deviations obtained varied from 0.02 to 0.41 cps. and the relative difference-limens, [Formula: see text], computed from the average deviations, were from 0.005 to 0.024.