The sequence of neurophysiological processes elicited in the auditory system by a sound is analyzed in search of the stage at which the processes carrying sensory information cross the borderline beyond which they directly underlie sound perception. Neurophysiological data suggest that this transition occurs when the sensory input is mapped onto the physiological basis of sensory memory in the auditory cortex. At this point, the sensory information carried by the stimulus-elicited process corresponds, for the first time, to that contained by the actual sound percept. Before this stage, the sensory stimulus code is fragmentary, lacks the time dimension, cannot enter conscious perception, and is not accessible to top-down processes (voluntary mental operations). On these grounds, 2 distinct stages of auditory sensory processing, prerepresentational and representational, can be distinguished.

The concept of auditory stimulus representation in cognitive neuroscience.

Although most recent multitalker research has emphasized the importance of binaural cues, monaural cues can play an equally important role in the perception of multiple simultaneous speech signals. In this experiment, the intelligibility of a target phrase masked by a single competing masker phrase was measured as a function of signal-to-noise ratio (SNR) with same-talker, same-sex, and different-sex target and masker voices. The results indicate that informational masking, rather than energetic masking, dominated performance in this experiment. The amount of masking was highly dependent on the similarity of the target and masker voices: performance was best when different-sex talkers were used and worst when the same talker was used for target and masker. Performance did not, however, improve monotonically with increasing SNR. Intelligibility generally plateaued at SNRs below 0 dB and, in some cases, intensity differences between the target and masking voices produced substantial improvements in performance with decreasing SNR. The results indicate that informational and energetic masking play substantially different roles in the perception of competing speech messages.

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Informational and energetic masking effects in the perception of multiple simultaneous talkers.

This book is about the processing of information in face-to-face communication when a speaker makes both audible and visible information available to a perceiver. Both auditory and visual sources of information are evaluated and integrated to achieve speech perception. The evaluation of the information source provides information about the strength of alternative interpretations, rather than just all-or-none categorical information, as claimed by “categorical perception” theory. Information sources are evaluated independently; the integration process insures that the least ambiguous sources have the most influences on the judgment. Similar processes occur in a variety of other behaviors, ranging from personality judgments and categorization to sentence interpretation and decision making. The experimental results are consistent with a fuzzy logical model of perception, positing three operations in perceptual (primary) recognition: feature evaluation, feature integration, and pattern classification. Continuously valued features are first evaluated, then integrated and matched against prototype descriptions in memory; finally, an identification decision is made on the basis of the relative goodness-of-match of the stimulus information with the relevant prototype descriptions.

Speech Perception By Ear and Eye: A Paradigm for Psychological Inquiry

On short and long auditory stores.

Spatial separation of speech and noise in an anechoic space creates a release from masking that often improves speech intelligibility. However, the masking release is severely reduced in reverberant spaces. This study investigated whether the distinct and separate localization of speech and interference provides any perceptual advantage that, due to the precedence effect, is not degraded by reflections. Listeners’ identification of nonsense sentences spoken by a female talker was measured in the presence of either speech-spectrum noise or other sentences spoken by a second female talker. Target and interference stimuli were presented in an anechoic chamber from loudspeakers directly in front and 60 degrees to the right in single-source and precedence-effect (lead-lag) conditions. For speech-spectrum noise, the spatial separation advantage for speech recognition (8 dB) was predictable from articulation index computations based on measured release from masking for narrow-band stimuli. The spatial separation advantage was only 1 dB in the lead-lag condition, despite the fact that a large perceptual separation was produced by the precedence effect. For the female talker interference, a much larger advantage occurred, apparently because informational masking was reduced by differences in perceived locations of target and interference.

The role of perceived spatial separation in the unmasking of speech.

This is the second in a series of articles in human listeners’ abilities to discriminate between word‐length tonal sequences, or ’’patterns.’’ The first article reported that frequency resolution, by highly trained listeners, is four to five times more accurate for high‐frequency, late‐occurring components of such sequences than for low−frequency early components [Watson, Kelly, and Benbasset, J. Acoust. Soc. Am. 57, 1175–1185 (l975)]. These effects, which are similar to described as ’’recognition masking’’ or ’’informational masking’’ by other authors, have now been shown to be strongly dependent on the degree of trial‐to‐trial stimulus uncertainty of the psychophysical procedure in which they are measured. When stimulus uncertainty is reduced to its psychophysical minimum, frequency resolution for any component of a tonal sequence is only slightly less accurate than for isolated tones. Previous reports of recognition masking this may reflect limitations imposed by those more dynamic parts of the sensory...

Factors in the discrimination of tonal patterns. II. Selective attention and learning under various levels of stimulus uncertainty

Factors which determine the discriminability of tonal sequences, or patterns, were investigated in five experiments. The patterns were generally sequences of ten 40‐msec tonal components, which ranged in frequency from 256 to 900 Hz, or from 500 to 1500 Hz, in equi‐log intervals. Highly trained (15 to 60 h of training prior to collecting experimental data) listeners’ abilities to detect changes in the frequency of single tonal components in these patterns were measured using a same–different psychophysical method. The just‐detectable values of Δf (d′=1.0) were only slightly larger than for single 40‐msec tones presented in isolation for tonal components at the end of the temporal sequences (a ’’recency’’ effect). Performance was systematically worse for earlier components, the just‐detectable Δf increasing by four to five times from the end of the pattern to the beginning (no ’’primacy’’ effect). The ’’recency’’ effect was interpreted as a matter of later arriving components interfering with frequency res...

Henry W. Wroton

Papers

Factors in the discrimination of tonal patterns. II. Selective attention and learning under various levels of stimulus uncertainty

Factors in the discrimination of tonal patterns. I. Component frequency, temporal position, and silent intervals.