How infants use vision for grasping objects.

The role of vision was examined as infants prepared to grasp horizontally and vertically oriented rods. Hand orientation was measured prior to contact to determine if infants differentially oriented their hands relative to the object's orientation. Infants reached for rods under different lighting conditions. Three experiments are reported in which (1) sight of the hand was removed (N = 12), (2) sight of the object was removed near the end of the reach (N = 40, including 10 adults), and (3) sight of the object was removed prior to reach onset (N = 9). Infants differentially oriented their hand to a similar extent regardless of lighting condition and similar to control conditions in which they could see the rod and hand throughout the reach. In preparation for reaching, infants may use the current sight of the object's orientation, or the memory of it, to orient the hand for grasping; sight of the hand had no effect on hand orientation.

The acoustic bases for gender identification from children's voices.

The purpose of this study was to examine the acoustic characteristics of children's speech and voices that account for listeners' ability to identify gender. In Experiment I, vocal recordings and gross physical measurements of 4-, 8-, 12-, and 16-year olds were taken (10 girls and 10 boys per age group). The speech sample consisted of seven nondiphthongal vowels of American English (/ae/ "had," /E/ "head," /i/ "heed," /I/ "hid," /a/ "hod," /inverted v/ "hud," and /u/ "who'd") produced in the carrier phrase, "Say /hVd/ again." Fundamental frequency (f0) and formant frequencies (F1, F2, F3) were measured from these syllables. In Experiment II, 20 adults rated the syllables produced by the children in Experiment I based on a six-point gender rating scale. The results from these experiments indicate (1) vowel formant frequencies differentiate gender for children as young as four years of age, while formant frequencies and f0 differentiate gender after 12 years of age, (2) the relationship between gross measures of physical size and vocal characteristics is apparent for at least 12- and 16-year olds, and (3) listeners can identify gender from the speech and voice of children as young as four years of age, and with respect to young children, listeners appear to base their gender ratings on vowel formant frequencies. The findings are discussed in relation to the development of gender identity and its perceptual representation in speech and voice.

A longitudinal investigation of infant auditory sensitivity.

The behavioral evaluation of hearing in very young infants has been fraught with procedural and interpretive problems. Despite the introduction of current physiological techniques of estimating hearing sensitivity, such as otoacoustic emissions and auditory brainstem-evoked responses, behavioral hearing assessment of young infants remains of interest to researchers of infant behavior and to clinicians who need to use a battery of tests in their assessment of infant hearing. The objective of this study was to provide the first longitudinal investigation of infant auditory sensitivity, using a new procedure for behavioral testing of neonates and infants. Behavioral responses to speech noise stimuli were obtained monthly from birth to 12 months of age. During each trial, the signal increased from an inaudible level in 2-dB steps until the infant responded. Therefore, a threshold estimate was obtained on each trial, and the average threshold could be computed across trials within a test session. Threshold estimates were in good agreement with previously reported infant behavioral thresholds based on cross-sectional designs. The age-related changes in threshold were fit with exponential functions for individual infants and for the group data. There was good agreement in the shape of these functions across infants, with asymptotic threshold level approached around 6 months of age. Therefore, this longitudinal study confirms that the age trend previously reported from cross-sectional findings is also observed in the development of individual infants.

Behavioral auditory assessment of young infants: methodological limitations or natural lack of auditory responsiveness?

The determination of auditory thresholds by means of behavioral techniques in young infants can be difficult. This could be the result of limitations in methodology, a lack of observable auditory responsiveness, or both. In the current study, 2- and 4-month old infants were tested under enhanced conditions for obtaining behavioral responses (i.e., salient auditory stimuli, reduced visual distractions, reinforced correct responses). A two-interval, forced-choice task with four intensity levels was used. Although a behavioral threshold was obtained for the 4-month-olds, threshold determination for the 2-month-olds remained elusive. In light of the current findings and previous studies of visual acuity of infants, these results suggest a lack of behavioral responsiveness to auditory stimuli for the younger infants rather than methodological limitations. With infants in the 2-month-old age range, clinical audiologists should expect few behavioral responses to auditory stimuli at intensity levels below those that elicit startle responses.

Brief antiepileptic drug withdrawal prolongs interval to next seizure.

OBJECTIVE: To evaluate the course of seizure control after reinstitution of antiepileptic drugs (AEDs) in patients whose AEDs were discontinued during inpatient EEG-video monitoring. METHODS: The authors studied prospectively patients with intractable epilepsy admitted for EEG-video monitoring with AED withdrawal. They examined seizure diaries in the 2 months preceding admission and recorded the number of seizures during hospitalization and for 2 months after discharge. They also recorded the interval between the last two seizures preceding admission (S-S pre), from the last seizure to admission (S-A), from discharge to the first seizure after discharge (D-S), and between the first and the second seizures following discharge (S-S post). RESULTS: Sixty patients qualified for the study. There was a significant decrease in seizure frequency in the 2 months after discharge compared with baseline (p = 0.02). For patients who had at least two seizures during follow-up, the mean D-S interval was significantly longer than mean S-S pre and S-S post (p < 0.005), whereas the latter two intervals were comparable. Prolongation of D-S was related to duration off AEDs and to the AED restarted, but not to the number or severity of seizures during monitoring. CONCLUSION: Seizure improvement after reinstitution of antiepileptic drugs (AEDs) is due primarily to prolongation of the interval from reinstitution of AEDs to the next seizure. This may reflect increased patient responsiveness to AED therapy after a drug "holiday" and has implications for experimental AED testing in the setting of presurgical evaluation.

One thousand intercarpal arthrodeses.

Limited wrist arthrodesis is a useful method for treating specific carpal disorders that maximizes residual wrist motion and strength while eliminating pain. Selective fusion of specific carpal units can be used in degenerative arthritis, rotary subluxation of the scaphoid, midcarpal instability, scaphoid nonunion, Kienbock's disease, and congenital synchondrosis or partial fusion of specific carpal joints. This report presents our experience with more than 1000 limited wrist arthrodeses, and provides a review of the indications and technical considerations for specific intercarpal fusions, and subsequent results. To date this is the largest series of intercarpal arthrodeses and the study has demonstrated that these techniques are reliable and effective in dealing with a wide range of wrist disorders.

Visual control of reaching and grasping in infants.

The role of visual input during reaching and grasping was evaluated. Groups of infants (5, 7, and 9 months old) and adults reached for an illuminated object that sometimes darkened during the reach. Behavioral and kinematic measures were assessed during transport and grasp. Both infants and adults could complete a reach and grasp to a darkened object. However, vision was used during the reach when the object remained visible. Infants contacted the object more often when it remained visible, though they had longer durations and more movement units. In contrast, adults reached faster and more precisely during transport and grasp when the object remained visible. Thus, continuous sight of the object was not necessary, but when it was available, infants used it for contacting the object whereas adults used it to reach and grasp more efficiently.

Auditory perception of walls via spectral variations in the ambient sound field.

Individuals with visual disabilities often use their hearing in order to maintain a line of travel parallel to walls, such as when walking down a hallway or along the side of a building. Previous studies established that this ability depends on the sense of hearing, but the specific acoustic information has not been investigated. The present paper describes a model of how sound pressure builds up within a meter or so in front of a wall, particularly in the low frequency end of the sound spectrum. This buildup of sound pressure is based on ambient or "background" sound, not self-produced sound such as footsteps. The model leads to a prediction that walls are detected by means of a spectral shift toward low frequencies. This prediction was tested in three experiments, in which sighted adults listened for such spectral shifts. In each experiment, a threshold value was obtained corresponding to the farthest simulated distance from a wall that could be detected. Threshold values were in good agreement with previous observations of the distance at which pedestrians can utilize acoustic information from walls. There was no evidence that simulated listener motion enhanced perception of walls. The model underlying these experiments implies that the term echolocation carries inappropriate connotations about the auditory processes that are involved in walking along walls. It is suggested that a more apt description is that pedestrians listen for spatial variations in the structure of the ambient sound field.

Persistent or recurrent carpal tunnel syndrome following prior endoscopic carpal tunnel release.

A retrospective review of patients with carpal tunnel syndrome (CTS) identified 20 patients (26 wrists) who had persistent or recurrent CTS after having undergone endoscopic carpal tunnel release (ECTR). Seven wrists never had relief of the original CTS symptoms; for the remaining 19 wrists, the average time to recurrence of CTS following ECTR was 4.8 months. All cases recurred within 12 months from the ECTR. All but 1 patient reported nocturnal pain. All patients experienced morning numbness and stiffness. All wrists had positive Phalen's test results. Once diagnosed with persistent or recurrent CTS, each of the wrists underwent open carpal tunnel release (OCTR). Twenty-two wrists were available for follow-up, with all patients reporting greater satisfaction and relief after the OCTR compared with the ECTR. It is important to recognize that CTS may persist or recur after ECTR. These patients should be treated with OCTR to provide symptomatic relief and prevent the sequelae of ongoing CTS.

Spatial hearing in children with visual disabilities.

A study is reported of the effect of early visual experience on the development of auditory space perception. The spatial hearing of thirty-five children with visual disabilities (twenty-two with congenital total blindness) was compared with that of eighteen sighted children and seventeen sighted adults. The tests provided a comprehensive assessment of spatial-hearing ability, including psychophysical estimates of spatial resolution in the horizontal, vertical, and distance dimensions, as well as measures of reaching and walking to the locations of sound sources. The spatial hearing of the children with visual disabilities was comparable to or somewhat better than that of the sighted children and adults. This pattern held even when the group with visual disabilities was restricted to those children with congenital total blindness; in fact, some of those children had exceptionally good spatial hearing. These findings imply that the developmental calibration of human spatial hearing is not dependent on a history of visual experience. It seems likely that this calibration arises from the experience of changes in sound-localization cues arising from self-motion, such as turning the head or walking. As a practical matter, orientation and mobility instructors may reasonably assume that individuals with visual disabilities can use their hearing effectively in day-to-day travel situations.

Temporal processing in the aging auditory system.

Measures of monaural temporal processing and binaural sensitivity were obtained from 12 young (mean age = 26.1 years) and 12 elderly (mean age = 70.9 years) adults with clinically normal hearing (pure-tone thresholds < or = 20 dB HL from 250 to 6000 Hz). Monaural temporal processing was measured by gap detection thresholds. Binaural sensitivity was measured by interaural time difference (ITD) thresholds. Gap and ITD thresholds were obtained at three sound levels (4, 8, or 16 dB above individual threshold). Subjects were also tested on two measures of speech perception, a masking level difference (MLD) task, and a syllable identification/discrimination task that included phonemes varying in voice onset time (VOT). Elderly listeners displayed poorer monaural temporal analysis (higher gap detection thresholds) and poorer binaural processing (higher ITD thresholds) at all sound levels. There were significant interactions between age and sound level, indicating that the age difference was larger at lower stimulus levels. Gap detection performance was found to correlate significantly with performance on the ITD task for young, but not elderly adult listeners. Elderly listeners also performed more poorly than younger listeners on both speech measures; however, there was no significant correlation between psychoacoustic and speech measures of temporal processing. Findings suggest that age-related factors other than peripheral hearing loss contribute to temporal processing deficits of elderly listeners.

Measuring habituation in infants: an approach using regression analysis.

The effectiveness of different habituation criteria was examined by means of computer simulations. A criterion based on fitting a second-order polynomial regression function to the looking time data was described. This criterion produced more accurate estimation of looking times as well as higher experimental power for detecting novelty effects, compared to the traditional windowed running average criterion or to a criterion based on linear regression. The polynomial regression approach probably has this advantage because it utilizes all of the available looking time data, rather than just the data in the current windowed average, and because it is sensitive to nonlinear trends in looking time. This new habituation criterion is easy to implement on a laboratory computer, and it should increase session lengths by no more than one trial or so, compared to windowed average criteria. With regard to test-retest reliability, all of the habituation criteria that were evaluated appear to have low reliability on average, with high sample-to-sample variability. These undesirable reliability characteristics are attributable to the high variability of infants' attentional behavior.

The fate of teeth transfixed by osteosynthesis screws.

Rigid internal fixation with plates and screws for osteosynthesis of facial fractures and osteotomies in the cranio-maxillofacial skeleton is often undertaken in situations in which the exact position of the underlying tooth roots cannot be determined. Therefore, a screw may be inadvertently placed into a root. There is scant data in the literature addressing the consequences of tooth impingement. This 5-year retrospective study documents the long-term outcome of teeth transfixed by osteosynthesis screws in a series of 387 consecutive facial fractures at a Level I trauma center. The incidence of root impingement per screw was 0.47 percent (13 transfixed teeth per 2340+ screws). Mandibular teeth were more "at risk" than maxillary teeth by a ratio of 10:3. No transfixed teeth became infected or required extraction in this series. In conclusion, inadvertent tooth root impingement by osteosynthesis screws appears to have minimal adverse consequences.

Treatment of Kienböck's disease with scaphotrapezio-trapezoid arthrodesis.

The long-term results of 28 cases of Kienböck's disease treated with scaphotrapezio-trapezoid arthrodesis between 1980 and 1990 are presented. The average follow-up period was 51 months. Of these wrists, nine required late lunate excision for pain and limited motion; however, only three patients in the entire series required further wrist salvage procedures (wrist arthrodesis, proximal row carpectomy). At late follow-up examination, range of motion averaged 48 degrees in extension, 52 degrees in flexion, 11 degrees in radial deviation, and 27 degrees in ulnar deviation. Using a subjective pain relief rating scale, patients reported excellent results in 12 cases, good results in 9, fair results in 4, and poor results in 2 (1 case was omitted because of a coexisting different disease).

Tissue expansion for Apert's syndactyly.

Tissue expansion is useful in post-traumatic reconstruction in the upper extremity. Its use has also been proposed in congenital syndactyly. Expanded local skin flaps would in theory provide locally appropriate cover, obviating the need for skin grafts. We report a retrospective assessment of tissue expansion in the management of Apert's syndactyly. Despite theoretical benefits, tissue expansion significantly increased the required number of operations. The technique was associated with an unacceptable rate of complications, and generated inadequate skin flaps, and web spaces requiring a higher rate of revision than traditional techniques. Despite expectations, tissue expansion for Apert's syndactyly proved disappointing and is not advocated.

Calibration of human locomotion and models of perceptual-motor organization.

People coordinate the force and direction of skilled actions with target locations and adjust the calibrations to compensate for changing circumstances. Are the adjustments globally organized (adjusting a particular action to fit a particular circumstance would generalize to all actions in the same circumstance); anatomically specific (every effector is adjusted independently of others); of functional (adjustments would generalize to all actions serving the same goal and generating the same perceptible consequences)? Across 10 experiments, changes in the calibration of walking, throwing, and turning-in-place were induced, and generalization of changes in calibration to functionally related and unrelated actions were tested. The experiments demonstrate that humans rapidly adjust the calibration of their walking, turning, and throwing to changing circumstances, and a functional model of perceptual-motor organization is suggested.

Contribution of listeners' approaching motion to auditory distance perception.

Of the several sources of acoustic information for distance perception, those arising from motion of the listener or sound source have received little attention. This motion-related information (recently called acoustic tau) is described, and experiments evaluating its utilization are presented. Accuracy and consistency at walking to the locations of briefly presented sounds were better when people listened while walking than while standing still. Manipulations of the sound to simulate shorter or longer target distances produced appropriate undershooting but not overshooting. The results indicate that people use motion-related acoustic information about distance to guide their locomotor actions, although they do not take full advantage of this information.

MRI asymmetries and language dominance.

OBJECTIVE: To examine the relationship between language dominance, as measured by Wada testing, and hemispheric asymmetries on MR brain images. BACKGROUND: A previous report that did not include verification of language dominance compared the length of the planum temporale with hemispheric asymmetries seen on CT and inferred that occipital lobe asymmetry is related to language dominance. METHODS: Language dominance was identified by the Wada test in 57 patients evaluated for surgical treatment of epilepsy. Fifty-five had an MRI scan that allowed accurate measurement. In a blinded fashion, two examiners independently measured bilateral frontal, parietal, and occipital lobe lengths on MR scan for each patient. Measurements of asymmetries were compared with language dominance established by the Wada test. RESULTS: Reliability of measurement between the examiners was 97%. Asymmetry of the occipital lobe length on MR scan 10 mm above the tentorium was the only measurement significantly related to language dominance (p < 0.01). Occipital lobe length was longer on the left in 19 (40%) and on the right in 10 (21%) patients with left dominance. The right lobe was longer in six of seven (86%) patients with bilateral dominance. One patient with right hemisphere dominance had a longer left lobe. None of the measurements significantly related to handedness. CONCLUSION: Asymmetries of occipital lobe length relate to language dominance, but such dominance cannot be reliably identified by MR in an individual patient.

Scapholunate advanced collapse wrist salvage.

Patients with scapholunate advanced collapse (SLAC) wrist do not have to undergo total wrist arthrodesis; the SLAC pattern spares the radiolunate articulation, providing a basis for salvage. We report the results of 100 cases in which a technique comprised of scaphoid excision and limited wrist arthrodesis was used. The average followup period of 44 months revealed excellent functional status and a high rate of patient satisfaction. The majority of employed patients were able to return to their original jobs, and many chose to resume wrist-related recreational activities. Pain relief was good to excellent in most cases. Extension/flexion averaged 72 degrees (53% of a normal opposite wrist), radioulnar deviation 37 degrees (59%), and grip strength 80% of the opposite side. X-ray films revealed only two instances of radiolunate destruction, both in conjunction with ulnar translation of the carpus. The other 98 patients demonstrated a well-preserved radiolunate joint regardless of followup interval. Complications were few. Nonunion occurred in three cases. A dorsal impingement of the capitate and radius (12%) was felt to be technique-related and avoidable by careful capitolunate alignment.