James R. Lackner

Resolving ambiguity: Effects of biasing context in the unattended ear☆

Abstract Ambigous sentences and a disambiguating context sentence were dichotically presented to subjects who were instructed to attend to the channel over which the ambiguous sentences were presented. Subjects were required to paraphrase the sentence in the attended channel immediately upon its presentation. The disambiguating material (in the unattended channel) was presented at a level 5 to 10 db less intense than the attended channel; in post-test reports subjects were unable to produce any information about the content of the unattended channel. Nonetheless, for four types of ambiguity tested, the bias contexts significantly influenced the interpretation of the ambiguous sentences. This result is taken to indicate both that there is structural analysis of the material in the unattended channel and that, during their input, multiple readings are computed for ambiguous sentences.

Alterations in auditory fusion thresholds after cerebral injury in man

Abstract Patients with penetrating wounds of the left cerebral hemisphere have abnormal fusion thresholds for dichotically presented clicks even if tested 20 years after the trauma. At temporal separations at which normal listeners report two clicks, these patients report hearing a single click. This diminished temporal resolving power of patients with left posterior cerebral lesions is most pronounced in those who are deemed dysphasic.

The underlying structures of sentences are the primary units of immediate speech processing

Two studies of the subjective location of clicks in spoken sentences indicate: (1) within-clause phrase structure boundaries do not significantly affect the segmentation of spoken sentences; (2) divisions between underlying structure sentences determine segmentation even in the absence of corresponding explicit clause divisions in the surface phrase structure. These results support a model of speech processing according to which listeners actively segment and organize spoken sequences into potential underlying syntactic structures.

Human orientation and movement control in weightless and artificial gravity environments

Abstractu2002Our goal is to summarize what has been learned from studies of human movement and orientation control in weightless conditions. An understanding of the physics of weightlessness is essential to appreciate the dramatic consequences of the absence of continuous contact forces on orientation and posture. Eye, head, arm, leg, and whole body movements are discussed, but only experiments whose results seem relatively incontrovertible are included. Emphasis is placed on distinguishing between virtually immediate adaptive compensations to weightlessness and those with longer time courses. The limitations and difficulties of performing experiments in weightless conditions are highlighted. We stress that when astronauts and cosmonauts return from extended space flight they do so with both physical ”plant” and neural ”controller” structurally and functionally altered. Recent developments in adapting humans to artificial gravity conditions are discussed as a way of maintaining sensory-motor and structural integrity in extended missions involving transitions between different force environments.

Some Sensory and Motor Factors Influencing the Control and Appreciation of Eye and Limb Position

SummarySome aspects of the manner in which the central nervous system uses sensory information for the guidance of eye and arm movements were investigated. When subjects experience apparent motion of their restrained forearm, induced by vibration of their biceps muscle in the dark, they are able to pursue with their eyes at least part of this “motion” and to point with their nonvibrated limb to the apparent location of the vibrated arm. The presence of a small target light on the vibrated hand limits the extent of illusory change in limb position and results in illusory motion of the target light in the same direction as the arm motion. When asked to indicate the spatial position of the light or hand, subjects still point with their nonvibrated arm to the apparent locations. Although visual pursuit of the illusory motion of the forearm can still be elicited in the presence of the target light on the hand, the subjects eyes remain steadily fixating the stationary target light when they are instructed to track its illusory motion. These findings demonstrate that sensory and motor factors affecting the perception of visual direction and the guidance of arm and eye movements can be differentially employed at several levels of central nervous control.

A developmental study of language behavior in retarded children

Abstract The purpose of this study was to achieve a slow motion perspective of normal language development by studying retarded children of different mental ages. Results from a variety of language tasks were used to develop transformational grammars which described the language behavior of each child as a self-contained system. Developmental trends were noted by comparing grammars of different complexity. The grammars of the retarded children are subsets of an adult grammar. They are very general, non-specific, and lack context sensitivity at the phrase-structure as well as the transformational level. The grammars of the retardates with higher mental ages begin to take on the specificity and wide range of applicability so characteristic of the adult grammar.

Adaptation to visual and proprioceptive rearrangement - Origin of the differential effectiveness of active and passive movements

In Experiment 1, subjects exposed to a discordance between the visual and ”proprioceptive” locations of external targets were found to exhibit aftereffects when later pointing without sight of their hands at visual targets. Aftereffects occur both when the discordance is introduced in the traditional fashion by displacing the visual locations of targets and when the proprioceptive locations of targets are displaced. These observations indicate that there is nothing unique about the visual rearrangement paradigm—the crucial factor determining whether adaptation will be elicited is the presence of a discordance in the positional information being conveyed over two different sensory modalities. In a second experiment, the effectiveness of active and passive movements in eliciting adaptation was studied using an experimental paradigm in which subjects were exposed to a systematic discordance between the visual and proprioceptive locations of external targets without ever being permitted sight of their hands; a superiority of active movements was observed, just as is usually found in visual rearrangement experiments in which sight of the hand is permitted. Evidence is presented that the failure of passive movements to elicit adaptation is related to a deterioration in accuracy of position sense information during passive limb movement.

Localization of the subjective vertical during roll, pitch, and recumbent yaw body tilt

Localization of the subjective vertical during body tilt in pitch and in roll has been extensively studied because of the relevance of these axes for aviation and control of posture. Studies of yaw orientation relative to gravity are lacking. Our goal was to perform the first thorough evaluation of static orientation in recumbent yaw and to collect as efficiently as possible roll and pitch orientation data which would be consistent with the literature, using the same technique as our yaw tests. This would create the first comprehensive, coherent data set for all three axes suitable for quantitative tri-dimensional modeling of spatial orientation. We tested localization of the vertical for subjects tilted in pitch (−100° to +130°), in roll (−90° to +90°), and in yaw while recumbent (−80° to +80°). We had subjects point a gravity-neutral probe to the gravitational vertical (haptically indicated vertical) and report verbally their perceived tilt. Subjects underestimated their body tilts in recumbent yaw and pitch and overestimated their tilts in roll. The haptic settings for pitch and roll were consistent with data in the literature obtained with haptic and visual indications. Our data constitute the first tri-dimensional assessment of the subjective vertical using a common measurement procedure and provide the basis for the tri-axial modeling of vestibular function presented in the companion paper.

Visual direction depends on the operation of spatial constancy mechanisms: the oculobrachial illusion

Abstract Subjects fixating a target light attached to their stationary hand saw it move when illusory motion of their arm was induced by muscle vibration. During the experienced visual motion and change in visual direction of the target light, their eyes maintained steady fixation. The existence of an ‘oculobrachial ilusion’ provides evidence that visual direction depends on the operation of a spatial constancy mechanism interrelating sensory information about the external environment and the moment-to-moment postural configuration of the body.

Perceived self-motion elicited by postrotary head tilts in a varying gravitoinertial force background

We measured the effects of postrotary head tilts on the perceived duration and the apparent axis of illusory self-rotation experienced following counterclockwise body rotation in high (1.8 G), normal (1 G), and low (0 G) gravitoinertial force environments. In the absence of head movements, the duration of illusory afterrotation was shorter in 0 G and 1.8 G than in 1 G, and it was further shortened by 40° pitch-back head movements in 1 G and 1.8 G. Clockwise illusory afterrotation about the torso’s verticalz-axis was always experienced in trials without postrotary head tilts. In trials with head movements, half the subjects experienced no change in this pattern; however, half experienced transient rightward roll of the torso’sz-axis, which remained the rotation axis. The duration and extent of apparent roll were greater in 0 G and smaller in 1.8 G than in 1 G. We provide a functional explanation for the tendency for perceived self-rotation to be determined relative to the torso and to the gravitoinertial vertical rather than solely in relation to head position and head-fixed angular velocity sensors.