Infants' pitch perception: masking by low- and high-frequency noises.

The present research employed an operant conditioning procedure typically used with infants to test noise masking of pure tones and tonal complexes in adults and in 7-month-old infants. Adults and infants were presented with either pure tones of 160 and 200 Hz or harmonic tonal complexes with pitches equivalent to 160 and 200 Hz. The tonal complexes did not contain energy at the fundamental frequency. After learning these tasks, subjects in the tonal complex group categorized spectrally varying tonal complexes according to the pitch of the missing fundamental. Stimuli were subsequently presented in combination with either a low- or a high-frequency noise. Both age groups successfully discriminated pure tones when combined with a high-frequency noise but not when combined with a low-frequency noise in the same frequency range as the pure tone. Infants, like adults, successfully categorized harmonic tonal complexes based on the pitch of the missing fundamental when those stimuli were combined with a low-frequency noise in the range of the missing fundamental but not when combined with a high-frequency noise which covered the frequency range of the harmonics themselves. These results suggest that infants rely primarily on a central process and not peripherally generated combination tones to hear the pitch of the missing fundamental.

Effects of fermentation time on in vivo/in vitro relationships.

The effects of six fermentation times, 24 through 84 h at 12 h intervals, were studied on in vivo/in vitro relationships and repeatability and variability of in vitro technique. Three stages of maturity each of bermudagrass, bahiagrass, rye-grass, sorghum-sudan, alfalfa, and orchardgrass were used. For one fermentation time for all types of forages, a 48-h fermentation demonstrated the smallest variation among runs and the least run X forage interaction. However, the optimum fermentation for perennials as a group was 60 h; and for annuals, legumes, and temperate grasses it was 36 h. Further studies in vitro compared a 48-h fermentation for all types of forage with 36 h for annuals and 60 h for perennials. Forty-eight forages, including 20 annuals and 28 perennials, were digested in vitro during three runs. With the 48-h fermentation, forages accounted for 86.43% of the total variation, runs 6.80%, and run X forage interaction 6.44%. Variation due to runs was reduced to .33%, and run X forage interaction to .90%, for a combined 36- and 60-h fermentation for annuals and perennials, respectively. Variation due to forage was increased to 98.53%.