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Investigates production and cost effects of teaching in radiology departments. If students are substitutes for physicians, production costs may be less in teaching than in non-teaching hospitals for a given level of output. Empirical results for Veterans Administration hospitals suggest that teaching reduces costs for most radiology procedures. If teaching can reduce costs of primary products, teaching hospitals may be able to provide a given program of patient care at lower costs than non-teaching hospitals. However, costs might still be higher at teaching hospitals than non-teaching hospitals because of differences in case mix, medical techniques, or quality of care.

The high-frequency limit of phase-locking has been measured in fibres of the auditory nerve in the guinea-pig. It is shown that phase-locking begins to decline at about 600 Hz and is no longer detectable above 3.5 kHz which is about 1 octave lower than in the cat, squirrel monkey and some birds. Direct measurements of the cochlear afferent fibre synaptic delay are consistent with indirect estimates from phase-locking, both giving values of 0.7-0.8 ms. Measurements of the receptor potentials of inner hair-cells in the guinea pig cochlea indicate that as the stimulus frequency is increased there is a progressive decrease in the a.c. component compared to the steady depolarization. The cause of this decline is the low-pass filtering of the a.c. component by the hair-cell membrane. The cut-off and slope of the decline in the a.c. component is consistent with the suggestion that this process is the limiting factor in cochlear nerve fibre phase-locking. The implications of these findings for interspecies variation in phase-locking cut-off, for cochlear mechanisms and for the encoding of complex sounds are discussed.

Rate-intensity functions (RIFs) were generated in response to characteristic frequency (CF) tones presented alone and in the presence of broadband noise for neurons in the central nucleus of the inferior colliculus (IC) of the anesthetized guinea pig. Seventy-six percent of the RIFs to CF tones were monotonic (some showing incomplete saturation), and 24% were nonmonotonic. The RIFs to continuous noise were more nonmonotonic than those to CF tones. In continuous or gated noise, the dynamic portion of the RIF to a tone was shifted to a higher tone level, with little change in the dynamic range. Above a threshold noise level, the shift was a linear function of noise level with slope 0.97. Little shift occurred when the noise was inversely gated with respect to the tone burst, suggesting that the underlying mechanism is suppression rather than adaptation. For 63% of units, the maximum discharge rate to a tone in low levels (less than 0-dB spectrum level) of noise (including inversely gated) was greater than to the tone alone. Although many of the effects of noise in the IC reflect peripheral mechanisms, they are supplemented by centrally based processes which enhance the detectability of tone intensity increments in the presence of noise.

The frog ear can be modelled as two coupled eardrums with an additional sound pathway through the mouth cavity. In a previous version of this model, with realistic parameters, we were able to account very well for empirical measurements of the eardrum vibration under free- and closed-field acoustic conditions. This earlier model does not, however, adequately predict the directional characteristics of the frog ear as determined empirically. In this paper we present a modified model which will account for the directionality together with the free- and closed-field frequency responses, and which is also consistent with anatomical considerations.

Silurian outcrops, not previously recorded from central Texas, have been identified from the Llano uplift, where they occur in collapse structures within the Lower Ordovician Honeycut Formation of the Ellenburger Group. The formation is a pinkish-gray granular limestone, contains fossils of probable Wenlock age, and is named the Starcke Limestone.