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Here, we present results of quantum cascade laser lifetime tests under various aging conditions including an accelerated life test. The total accumulated life time exceeds 1.5 x 106 device hours. The longest single device aging time was 46500 hours without failure in the room temperature aging test. Four failures were found in a group of 19 devices subjected to the accelerated life test with a heat-sink temperature of 60 °C and a continuous-wave current of 1 A. Failure mode analyses revealed that thermally induced oxidation of InP in the semi-insulating layer is the cause of failure. An activation energy of 1.2 eV is derived from the dependence of the failure rate on laser core temperature. The mean time to failure of the quantum cascade lasers operating at a typical condition with the current density of 5 kA/cm² and heat-sink temperature of 25 °C is expected to be 809 000 hours. [ABSTRACT FROM AUTHOR]

Preliminary findings in our laboratory have suggested that the 'lag effect' [M. Studdert-Kennedy, D. Shankweiler, and S. Schulman, J. Acoust. Soc. Am. 48, 599-602 (1970); C.I. Berlin, S. Lowe-Bell, J.K. Cullen Jr., and C.L. Thompson, J. Acoust. Soc. Am. 53, 699-708 (1973)] may change at intensities below 75 dB SPL. An experiment is currently underway studying the 'lag effect' at intensities of 50-80 dB SPL and preliminary data suggest there may be a lead effect at low intensities which reverses as both competing syllables are presented at higher intensities. [Supported by National Institutes of Health, USPHS Grant No. NH 11647-01.] [ABSTRACT FROM AUTHOR]

Measuring tinnitus in laboratory animals is difficult, involving weeks or months of operant training. Preliminary data suggest that rapid screening for tinnitus in rats can be accomplished using an unconditioned acoustic startle reflex. In control animals, a gap in an otherwise constant acoustic background inhibits a subsequent startle response to a sound impulse. If, however, the background signal is qualitatively similar to the animal’s tinnitus, poorer detection of the gap and less inhibition of the startle might be expected. Fourteen animals with putative tinnitus at 10 kHz and 13 control animals were tested for gap detection using three different background signals: broadband noise, and filtered bandpass noise centered either at 16 kHz (15.5–16.5 kHz) or at their suspected tinnitus locus of 10 kHz (9.5–10.5 kHz). As predicted, animals with evidence of tinnitus exhibited significantly worse gap detection at 10 kHz, and were not significantly different than control animals at 16 kHz and broadband noise. These results suggest a new methodology for rapidly detecting tinnitus in individual animals. Equipment donated by Hamilton-Kinder Inc Behavioral Testing Systems in the memory of SIU graduate Dorothy Jean Kinder (Walker). [Work supported by NIH grants AG023910-01 (JT), DC4830 (TB & CB), and DC00151 (DC).] [ABSTRACT FROM AUTHOR]

Data were gathered from four well-practiced subjects in a 2AFC paradigm which was subject driven, and allowed as many repeats of the stimulus pair as the subject requested prior to making his response. The stimuli consisted of the six stop-consonants followed by the vowel /a/. These natural speech CV's have served as stimuli in numerous dichotic speech perception studies. The results indicated that when the stimuli were separated by no more than 15 msec, the subjects could be divided into two homogeneous groups. One group was able to reliably determine a parallel pair of perceptual onset functions (one for each ear) which were of moderate slope and were separated by approximately 13 msec. The other group of subjects showed a reversal of the ear asymmetry and their perceptual onset functions had a zero slope. The results will be discussed in terms of its relevance to the temporal variables involved in dichotic CV experiments. [Supported by National Institutes of Health, USPHS Grant No. NS 11647-03.] [ABSTRACT FROM AUTHOR]

Reaction times for two right handed subjects who received 6000 trials of dichotic CVs were obtained under response conditions involving the left hand, right hand, and axial movements [Geschwind, Am. Sci. 63 (2), 188-195 (1975)]. The simultaneous CVs were presented in a target-challenge paradigm (Berlin et al., IEEE Trans. Audio Electroacoust. AU-21, 189 (1973)]. The results indicated that when the targets were presented to the right ear, the latencies were shorter (150+ msec) than when presented to the left ear. The large and stable differences in latencies remained invariant with the mode of response. Phonetic effects involving manner and place of articulation will be discussed. The relationship between the obtained measures of latency and percent correct are also included. [Supported by National Institutes of Health, USPHS Grant No. NH 11647-02.] [ABSTRACT FROM AUTHOR]

Synthetic CVs competed against 'bleats' (second and third formant transitions, both kindly supplied to us by D. Pisoni and colleagues) alternately in the right and left ears of 10 subjects. Both right and left ears were suppressed by the presence of the bleat in the other ear, but the left ear suffered more interference than the right ear. The nonsemantic and unintelligible nature of the bleats, coupled with their ability to generate an REA when competing against CVs, heightens the importance of acoustic factors in the dichotic right-ear advantage for CVs. However, the results do not suggest that there are no other contributing factors to the REA, and should not be so construed. [Supported by National Institutes of Health, USPHS Grant No. NH 11647-01.] [ABSTRACT FROM AUTHOR]

Eight normal subjects were tested in a dichotic consonant-vowel identification task where synthetic tokens of the stops + [æ] ranging in duration from 40 to 296 msec were used as challenges against 296-msec tokens from the same synthetic set. Subjects were required to identify both items in a dichotic pair. As challenge durations were reduced, their dichotic performance dropped paralleling monaural intelligibility, voiceless items being more severely affected than voiced items. Performance for the nonshortened items increased as the duration of the challenges dropped, in a manner not entirely reflecting the challenge intelligibility loss. Additionally, a 'backward-masking' effect of temporally remote vowel segments on competing consonant identification was clearly shown. [Supported by National Institutes of Health, USPHS Grant No. NH 11647-01.] [ABSTRACT FROM AUTHOR]

Normal subjects were presented simultaneously aligned consonant-vowel stimuli in three forced-choice dichotic experiments in which the information content of one signal was changed by (1) varying the intensity, (2) low-pass filtering, and (3) alterations in signal-to-noise ratios. The results of all three experiments were complementary. As signal characteristics were varied to produce a reduction of information to one ear, and thus a decrement in performance, an increment in performance of the unaltered ear was observed. The trade-off ratios of decrement and increment were such that total performance (summed ear scores) remained virtually constant. Dichotic ear effects (e.g., right ear outperforming left ear) appear to be orthogonal to this phenomenon. These observations indicate that perception of dichotically presented consonant-vowel depends upon the central additivity of information from two quasi-independent channels, overall performance being limited by the capacity of the central processor. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Previous data [S. S. Lowe, J. K. Cullen, Jr., C. I. Berlin, C. L. Thompson, and M. E. Willett, J. Speech Hearing, Res. 13, 812-822 (1970); C. I. Berlin, M. E. Willett, C. L. Thompson, J. K. Cullen, Jr., and S.S. Lowe, J. Acoust. Soc. Amer. 47, 75-76 (1970)] show that when the onsets of the six English stops are aligned in dichotic CV pairs, voiceless CVs are more intelligible than voiced. This experiment reports the effect of maintaining onset alignments but changing voicing onset times (VOT) of the syllables. Thus, two types of voiceless CVs (+60 and +90 msec VOT) and two types of voiced CVs (-30 and 0 VOT) competed with each other in a dichotic paradigm. Changing VOT for the voiceless items had little effect on overall intelligibility. Using a 0-msec VOT voiced item, however, generated greater probability that the voiceless dichotic items would be perceived correctly. The relationship of this observation to the 'lag effect' and suppression of one item by another will be discussed. [ABSTRACT FROM AUTHOR]

These data represent further analyses of experiments previously reported [C. I. Berlin, C. L. Loovis, S. S. Lowe, J. K. Cullen, Jr., and C. L. Thompson, J. Acoust. Soc. Amer. 48, 70-71 (1970)]. Analysis of the errors made by normal subjects reveal that at simultaneity unvoiced consonants are better perceived than voiced consonants, especially when the unvoiced compete with the voiced consonants. When two voiced consonants compete, the V-V competition yields intelligibility about as good as the U-U competition; however, when U and V compete, then the intelligibility of the unvoiced syllable goes up while the intelligibility of the voiced syllable drops. As time asynchronies are introduced, the intelligibility of the unvoiced consonants remains constant while the intelligibility of the voiced consonant in the competing pair increases until, by 90-msec temporal offset, intelligibility of both voiceless and voiced CVs are the same. A preliminary hypothesis on switching during analysis time will be presented. [ABSTRACT FROM AUTHOR]