1. Single-unit recordings were made in the auditory midbrain, the torus semicircularis (TS) of the northern leopard frog, to independently characterize the processing of different temporal attributes (signal duration, rise-fall time, and rate of amplitude modulation) of natural sounds and to investigate how these temporal variables interact to produce the observed responses to complex amplitude-modulated (AM) signals. Response functions, on the basis of mean spike count, were derived and categorized to describe the unit's temporal response characteristics to each of the variables. 2. To characterize the duration response functions, tone bursts of different durations (stimuli repeated at a constant repetition rate) at the unit's characteristic frequency (CF) and 10 dB above minimum threshold at CF (MT) were presented monaurally to the contralateral ear. The duration response function of a TS neuron was often related to the temporal discharge characteristics of the neuron. Increases in stimulus duration elicited an increase in spike counts (therefore, long-pass response function) from most neurons (74%) in the TS; 91% of these neurons showed tonic discharge patterns. Phasic-burst (PB) cells that were rapidly adapting showed long-pass duration response functions that were highly nonlinear, having peaks and notches embedded within the functions. On the other hand, one-third of phasic neurons tended to be insensitive to stimulus duration, giving similar spike counts in response to stimuli of greatly different durations (i.e., all pass). In the TS, some neurons (9%) only responded to a limited range of durations (i.e., band-duration pass), and still others showed a preference for shorter durations (9%; i.e., short pass); these were exhibited primarily by phasic and PB neurons. 3. To characterize the rise-fall time response functions, tone bursts having different rise-fall times were presented. The rise-fall time response functions of TS neurons had two distinct characteristics. The majority of tonic cells (91%), as well as some PB (38%) and phasic (29%) neurons, gave essentially invariant spike counts for all stimulus rise-fall times (i.e., all pass; 73% of neurons). Despite the relatively stable spike counts of neurons showing all-pass functions, the peristimulus time histograms (PSTHs) deriving from responses to slower rise-fall time stimuli exhibited a longer and somewhat more variable onset latency. About one-fourth (27%) of TS neurons, mostly phasic and PB neurons, showed higher spike counts for signals with rapid rise-fall times.(ABSTRACT TRUNCATED AT 400 WORDS)

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This paper presents a compact graphical method for comparing the performance of individual hearing impaired ͑HI͒ listeners with that of an average normal hearing ͑NH͒ listener on a consonant-by-consonant basis. This representation, named the consonant loss profile ͑CLP͒, characterizes the effect of a listener's hearing loss on each consonant over a range of performance. The CLP shows that the consonant loss, which is the signal-to-noise ratio ͑SNR͒ difference at equal NH and HI scores, is consonant-dependent and varies with the score. This variation in the consonant loss reveals that hearing loss renders some consonants unintelligible, while it reduces noise-robustness of some other consonants. The conventional SNR-loss metric ⌬SNR 50 , defined as the SNR difference at 50% recognition score, is insufficient to capture this variation. The ⌬SNR 50 value is on average 12 dB lower when measured with sentences using standard clinical procedures than when measured with nonsense syllables. A listener with symmetric hearing loss may not have identical CLPs for both ears. Some consonant confusions by HI listeners are influenced by the high-frequency hearing loss even at a presentation level as high as 85 dB sound pressure level.

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1. A midline region of brain dorsal and anterior to the corpus callosum, presumably anterior cingulate cortex, has been explored for its role in the production of vocalization in the mustached bat, Pteronotus p. parnelli. 2. Vocalizations elicited by microstimulation were virtually indistinguishable from natural biosonar sounds. The spectral content, relative intensity of harmonic components, and durations of emitted pulses are comparable to spontaneous emissions. 3. The frequencies of elicited vocalizations were within the range typically used by the mustached bat during Doppler-shift compensation. The frequency of the second-harmonic constant-frequency component (CF2) covered the range from 57-62 kHz, but was most commonly emitted at frequencies of 59-61 kHz. 4. An increase in the frequency of vocalizations over a number of consecutive pulses towards a steady-state plateau is evident in both spontaneous vocalizations and emissions elicited by microstimulation just above threshold. Increasing the stimulus intensity caused the frequency of emissions to approach the steady state more rapidly. 5. The anterior cingulate cortex appears to be organized topographically for increasing frequency of elicited biosonar sounds along a rostrocaudal axis. The area from which biosonar emissions were elicited was overrepresented for a 2 kHz band of frequencies just below the bats' CF2 resting frequency. Audible vocalizations with a complex spectrum resembling social cries can also be elicited by microstimulation, but only in an area that is adjacent and posterior to the biosonar region. 6. Some examples of both elicited and spontaneous vocalizations contained a relative intensity pattern of the harmonic components which deviated from the typical pattern. This suggests that mustached bats are capable of actively altering the spectrum of their pulses to subserve different tasks in echolocation.