Compensation for Auditory Re-Arrangement in Hand-Ear Coordination

Abstract

10 Ss pointed at concealed auditory targets while listening through a pseudophone which produced 20" functional rotation of the interaural axis. After short exposures listening to a sound source held in one hand while moving that hand about, large and significant corrective shifts in pointing were measured.Accurate spatially-oriented behavior requires the maintenance of a set of known and stable relationships between the observer and his perceptual world. W e have found it productive to perturb these relationships in order to study the nature and extent of the adaptation which occurs. Our recent work has emphasized auditory spatial orientation or auditorily guided motor behavior. W e have shown that ability to discriminate dichotic time differences deteriorates markedly during exposures to dichotic white noise (Freedman & Pfaff, 1962;Freedman & Zacks, 1964). Also under appropriate conditions, Ss tend to compensate (or correct) for pseudophonic displacements of the apparent locations of auditory stimuli (Freedman & Stampfer, 1964). All of these experiments required whole-body movement during the exposure period which is difficult to limit and control. It seemed desirable to have comparable experimencs involving more circumscribed sensorimotor systems. A procedure was therefore devised to study hand-ear coordination, i.e., reaching and pointing at a concealed auditory carget.Preliminary studies indicated that Ss would compensate significantly for 20" rotation of the interaural axis in hand-ear coordination if they simply listened while moving a hand-held sound source back and forth across the front of their bodies for a few minutes (Freedman & Gardos, 1965). Unfortunately, as in many sensorimotor adaptation studies, the intersubject variability was high; also we feared that response stereotypy had confounded the results. The present paper describes a replication of that work with improved procedures and controls.The experimenu were conducted in a small room ( 1 6 ft. X 7 ft. X 9 ft. high) whose walls and ceiling were covered with acoustic tile. S sat comfortably on a stool at

Lack of bilateral generalization of adaptation to auditory rearrangement

“…Although the data reflect a good deal of individual differences in magnitude of adaptation, a common observatlon in adaptation studies, the responses of most Ss are quite consistent. Systematic changes in ear-hand coordination follow exposure to auditory rearrangement, confirming earlier reports (Freedman et al, 1967;Mikaelian, 1969); however, these changes occur mostly in responses with the ipsilateral arm and, except for Table 1 TraDsfer of Adaptation to Rearranced Ear-Hand Coordination.…”

“…Typically, adaptation is produced by having a blindfolded S move a hand-held sound source while listening through pseudophones. The direction and magnitude of the differences between pre-and postpseudophone exposure measurements of ear-hand coordination are systematically related to the functional rotation of the interaural axis (Freedman et al, 1967, andMikaelian, 1969). Unlike viewing through prisms, S listening through pseudophones cannot resolve the imposed sensory transform.…”

Adapting to supernormal auditory localization cues. II. Constraints on adaptation of mean response

“…It is interesting to note that subjects, on average, adapted to the best-fit linear approximation of the nonlinear cue transformations used in the current experiments ͑although some systematic errors in localization judgments, due to the nonlinearity of the employed transformations, remained͒. In most previous studies of auditory adaptation, subjects appeared to adapt only partially to sensory rearrangements ͑e.g., see Freedman and Gardos, 1965;Stampfer, 1964a, 1964b;Freedman and Zacks, 1964;Held, 1955;Kalil and Freedman, 1967;Lackner, 1974;Mikaelian, 1974;Mikaelian and Russotti, 1972͒. This apparent failure to adapt completely may be the result of an inability to adapt perfectly to the type of transformation employed.…”

Effects of user training with electronically-modulated sound transmission hearing protectors and the open ear on horizontal localization ability

“…Pseudophones to modify the sound wave ' s entrance to the ear canal have been used to distort horizontal localization cues by rotating the horizontal axis 20 -30 ° to either the left or right (Canon, 1971;Freedman & Gardos, 1965;Freedman & Stampfer, 1964;Freedman et al, 1967;Held, 1955;Mikaelian, 1969). Use of the pseudophones with passive or active training allowed for various levels of adaptation within fi ve minutes to seven hours.…”