Nathaniel I. Durlach

Intensity Perception. I. Preliminary Theory of Intensity Resolution

An attempt is made to develop a quantitative theory of intensity resolution that is applicable to a wide variety of experiments on discrimination, identification, and scaling. The theory is composed of a Thurstonian decision model, which separates sensitivity from response bias, and an internal‐noise model, which separates sensory limitations from memory limitations. It is assumed that the subject has two memory operating modes, a sensory‐trace mode and a context‐coding mode, and that the use of these two modes is determined by the characteristics of the experiment. In one‐interval paradigms, it is assumed that the context‐coding mode is used, and the theory relates resolution to the total range of intensities in the stimulus set. In two‐interval paradigms, it is assumed that the two modes are combined, and the theory relates resolution to both the total intensity range and the duration between the two intervals. The theory provides, among other things, a new interpretation of the 7 ± 2 phenomenon.

Speaking Clearly for the Hard of Hearing I: Intelligibility Differences between Clear and Conversational Speech

The first paper of this series (Picheny, Durlach, & Braida, 1985) presented evidence that there are substantial intelligibility differences for hearing-impaired listeners between nonsense sentences...This paper is concerned with variations in the intelligibility of speech produced for hearing-impaired listeners under two conditions. Estimates were made of the magnitude of the intelligibility differences between attempts to speak clearly and attempts to speak conversationally. Five listeners with sensorineural hearing losses were tested on groups of nonsense sentences spoken clearly and conversationally by three male talkers as a function of level and frequency-gain characteristic. The average intelligibility difference between clear and conversational speech averaged across talker was found to be 17 percentage points. To a first approximation, this difference was independent of the listener, level, and frequency-gain characteristic. Analysis of segmental-level errors was only possible for two listeners and indicated that improvements in intelligibility occurred across all phoneme classes.

Note on informational masking (L)

Informational masking (IM) has a long history and is currently receiving considerable attention. Nevertheless, there is no clear and generally accepted picture of how IM should be defined, and once defined, explained. In this letter, consideration is given to the problems of defining IM and specifying research that is needed to better understand and model IM.

Manual discrimination of compliance using active pinch grasp: The roles of force and work cues

In these experiments, two plates were grasped between the thumb and the index finger and squeezed together along a linear track. The force resisting the squeeze, produced by an electromechanical system under computer control, was programmed to be either constant (in the case of the force discrimination experiments) or linearly increasing (in the case of the compliance discrimination experiments) over the squeezing displacement. After completing a set of basic psychophysical experiments on compliance resolution (Experiment 1), we performed further experiments to investigate whether work and/or terminal-force cues played a role in compliance discrimination. In Experiment 2, compliance and force discrimination experiments were conducted with a roving-displacement paradigm to dissociate work cues (and terminal-force cues for the compliance experiments) from compliance and force cues, respectively. The effect of trial-by-trial feedback on response strategy was also investigated. In Experiment 3, compliance discrimination experiments were conducted with work cues totally eliminated and terminal-force cues greatly reduced. Our results suggest that people tend to use mechanical work and force cues for compliance discrimination. When work and terminal-force cues were dissociated from compliance cues, compliance resolution was poor (22%) relative to force and length resolution. When work cues were totally eliminated, performance could be predicted from terminal-force cues. A parsimonious description of all data from the compliance experiments is that subjects discriminated compliance on the basis of terminal force.

MANUAL DISCRIMINATION OF FORCE USING ACTIVE FINGER MOTION

In these experiments, two plates were grasped between the thumb and forefinger and squeezed together along a linear track. An electromechanical system presented a constant resistance force during the squeeze up to a predetermined location on the track, whereupon the force effectively went to infinity (simulating a wall) or to zero (simulating a cliff). The task of the subject was to discriminate between two alternative levels of the constant resistance force (a reference level and a reference-plus-increment level). Results of these experiments indicate a just noticeable difference of roughly 7% of the reference force using a one-interval paradigm with trial-by-trial feedback over the ranges 2.5≤Fo≤10.0 newtons, 5≤D≤30 mm, 45≤S≤125 mm, and 25≤V≤160 mm/sec, whereFo is the reference force,D is the distance squeezed,S is the initial finger-span, andV is the mean velocity of the squeeze. These results, based on tests with 5 subjects, are consistent with a wide range of previous results, some of which are associated with other body surfaces and muscle systems and many of which were obtained with different psychophysical methods.

Presence in Shared Virtual Environments and Virtual Togetherness

This Forum article discusses the relationships among people, their avatars, and their virtual environment workstations in a shared virtual environment. It introduces the notion of togetherness, the sense of people being together in a shared space, which is the counterpart for shared VEs to the presence of an individual in a VE. The role of tactual communication is emphasized as being fundamental to togetherness.

Intensity perception. XIII. Perceptual anchor model of context‐coding

In our preliminary theory of intensity resolution [e.g., see N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372-383 (1969)], two modes of memory operation are postulated: the trace mode and the context-coding mode. In this paper, we present a revised model of the context-coding mode which describes explicitly a process by which sensations are coded relative to the context and which predicts a resolution edge effect [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483-502 (1972); J. E. Berliner, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am. 61, 1256-1267 (1977)]. The sensation arising from a given stimulus presentation is coded by determining its distance from internal references or perceptual anchors. The noise in this process, combined with the sensation noise, constitutes the limitation on resolution in the model. In the revised model the probability density functions of the decision variable are not precisely Gaussian (and cannot be expressed analytically in closed form). This paper outlines the predictions of the model for one-interval paradigms and for fixed-level two-interval paradigms and derives estimates of the values of model parameters.

Information transmission with a multifinger tactual display

In this work, the tactual information transmission capabilities of a tactual display designed to provide stimulation along a continuum from kinesthetic movements to cutaneous vibrations are assessed. The display is capable of delivering arbitrary waveforms to three digits (thumb, index, and middle finger) within an amplitude range from absolute detection threshold to about 50 dB sensation level and a frequency range from dc to above 300 Hz. Stimulus sets were designed at each of three signal durations (125, 250, and 500 msec) by combining salient attributes, such as frequency (further divided into low, middle, and high regions), amplitude, direction of motion, and finger location. Estimated static information transfer (IT) was 6.5 bits at 500 mseC., 6.4 bits at 250 mseC., and 5.6 bits at 125 msec. Estimates of IT rate were derived from identification experiments in which the subject’s task was to identify the middle stimulus in a sequence of three stimuli randomly selected from a given stimulus set. On the basis of the extrapolations from these IT measurements to continuous streams, the IT rate was estimated to be about 12 bits/seC., which is roughly the same as that achieved by Tadoma users in tactual speech communication.

Study of multichannel amplitude compression and linear amplification for persons with sensorineural hearing loss

Experiments were conducted on five listeners with sensorineural hearing impairments using two 16-channel, computer-controlled, amplitude compression systems, and four linear systems. One of the compression systems was designed to restore normal equal loudness contours, the other employed reduced high-frequency emphasis and reduced compression ratios. The linear systems differed only in their frequency-gain characteristics (orthotelephonic plus three characteristics with high-frequency emphasis that were expected to produce better results than orthotelephonic). In the main experiment, all systems were compared for each listener using nonsense CVC monosyllables and sentence materials spoken by male and female talkers and presented in quiet/anechoic and noisy/reverberant environments at the most comfortable level for each listener. The linear systems with high-frequency emphasis performed substantially better than the orthotelephonic system. Performance with compression was generally slightly worse than with linear amplification. Compression was superior to linear amplification only when speech materials with significant item-to-item level variation were used in quiet with subjects with more severe losses and when reduced input speech levels were used. To the extent that these two conditions represent real-life communication conditions, these results suggest that compression is preferable to linear amplification in a wearable hearing aid.

Manual discrimination and identification of length by the finger-span method

Experiments were conducted on length resolution for objects held between the thumb and forefinger. The just noticeable difference in length measured in discrimination experiments is roughly 1 mm for reference lengths of 10 to 20 mm. It increases monotonically with reference length but violates Weber’s law. Also, it decreases when the subject is permittedto maintain a constant finger span between trials; however, it tends to increase when the nondominant hand is used. As would be expected from studies of other stimulus dimensions in other sense modalities, resolution is considerably poorer in identification experiments than in discrimination experiments. For stimulus sets that cover a broad range (90 mm), the total information transfer is roughly 2 bits; for those that cover a relatively small range (18 mm), it is roughly 1 bit. The data are analyzed and interpreted using analysis techniques and models that have been used previously in studies of audition (e.g., Durlach &Braida, 1969).