Evaluation of two multichannel tactile aids for the hearing impaired

Abstract

Two multichannel tactile devices for the hearing impaired were compared in speech perception tasks of varying levels of complexity. Both devices implemented the "vocoder" principle in their stimulus processing: One device had a 16-element linear vibratory array worn on the forearm and displayed activity in 16 overlapping frequency channels; the other device delivered tactile stimulation to a linear array of 16 electrodes worn on the abdomen. Subjects were tested in several phoneme discrimination tasks, ranging from discrimination of pairs of words differing in only one phoneme under tactile aid alone conditions to identification of stimuli in a larger set under tactile aid alone, lipreading alone, and lipreading plus tactile aid conditions. Results showed both devices to be better transmitters of manner and voicing features of articulation than of place features, when tested in single-item tasks. No systematic differences in performance with the two devices were observed. However, in a connected discourse tracking task, the vibrotactile vocoder in conjunction with lipreading yielded much greater improvements over lipreading alone than did the electrotactile vocoder. One possible explanation for this difference in performance, the inclusion of a noise suppression circuit in the electrotactile aid, was evaluated, but did not appear to account for the differences observed. Results are discussed in terms of additional differences between the two devices that may influence performance.

Controller design and consonantal contrast coding using a multi-finger tactual display

“…The results of the two studies show similar performance: An average discriminability of 94% and dЈ of 3.5 were obtained in the present study when contrasting five voiced-unvoiced consonant pairs, indicating that the coding scheme used in Yuan, 2003 was a subset of the scheme used in the present study. The performance level obtained in the present study also appears to compare favorably with the results reported by earlier studies of tactual displays, where discrimination scores were generally less than 75% ͑Plant, 1989; Clements et al, 1988;Galvin et al, 1999;Waldstein and Boothroyd, 1995;Weisenberger et al, 1989;Summers et al, 2005͒. In addition to incorporating the amplitude information from low-and high-frequency speech bands, as in Yuan, 2003, our coding scheme displays energy information from the mid-frequency speech band in the form of temporal envelopes as well as low-frequency motion cues from the three speech bands to the corresponding fingerpads. To the best of our knowledge, this is the first time that low-frequency motion cues have been used to encode speech spectral information.…”

“…The pairwise discrimination performance of the manner of articulation and voicing features was satisfactory ͑71% for voicing and 80% for manner͒ but discriminability of place of articulation distinction was poorer, i.e., 66%. Even with the multi-channel spectral display of the Queen's vocoder studied by Weisenberger et al ͑1989͒, place of articulation was not discriminated as well as other features ͑65% for place compared to 75% for manner and 70% for voicing͒. In other studies, discriminability of place of articulation was at chance level ͑Waldstein and Boothroyd, 1995;Plant, 1989;Summers et al, 2005;Weisenberger and Percy, 1995;Galvin et al, 1999͒. Therefore, it appears that the present coding scheme was able to transmit the place of articulation feature more successfully than has been demonstrated previously.…”

“…By comparison, the estimated communication rates for speech transmission through artificial tactile aids are substantially below those of the Tadoma method ͑Reed and Durlach, 1998͒. The limited success demonstrated thus far with artificial tactual communication systems may be due to a variety of factors, including ͑1͒ the homogeneous nature of displays that utilize single or multiple actuators to deliver only high-frequency cutaneous stimulation, and ͑2͒ the use of body sites with relatively sparse nerve innervation, such as forearm, abdomen, or neck ͑Plant, 1989; Waldstein and Boothroyd, 1995;Weisenberger et al, 1989;Galvin et al, 1999;Summers et al, 2005͒. In contrast, Tadoma users have access to a rich set of stimulus attributes, including kinesthetic movements of the face and jaw, cutaneous vibrations at the neck, airflow at the lips, and muscle tensions in the face, jaw, and neck, which are received through the hands.…”

“…In addition to the tactile waveforms, the coding scheme monitored energy peaks within each band and presented this information as lowfrequency motional cues-extending the finger for highfrequency contents and flexing the finger for low-frequency contents in the corresponding finger band. These more pronounced representations of formant and formant transition cues were employed in an effort to improve the transmission of cues related to place of articulation, which have been poorly transmitted through previous tactile aids ͑Clements Weisenberger et al, 1989;Waldstein and Boothroyd, 1995;Plant, 1989;Summers et al, 2005;Weisenberger and Percy, 1995;Galvin et al, 1999͒. Acoustical analyses of plosive and fricative consonants have shown that place of articulation is well correlated with the frequency values of the first two formants ͑spectral peaks in the speech spectrum due to the shape of the mouth͒, F1 andF2, andtheir transitions ͑Ali et al, 2001a, 2001b;Jongman et al, 2000͒.…”

For speech perception by humans or machines, three senses are better than one

“…Reed [17], in this session, discusses Tadoma, a method used by a small number of deaf-blind people to perceive speech through their hands. Developments in artificial sensory substitution have afforded further evidence that speech can be perceived via touch [18,19,20,21,22].…”