The role of central and peripheral vision in perceiving the direction of self-motion.

Three experiments were performed to examine the role that central and peripheral vision play in the perception of the direction of translational self-motion, or heading, from optical flow. When the focus of radial outflow was in central vision, heading accuracy was slightly higher with central circular displays (10 degrees-25 degrees diameter) than with peripheral annular displays (40 degrees diameter), indicating that central vision is somewhat more sensitive to this information. Performance dropped rapidly as the eccentricity of the focus of outflow increased, indicating that the periphery does not accurately extract radial flow patterns. Together with recent research on vection and postural adjustments, these results contradict the peripheral dominance hypothesis that peripheral vision is specialized for perception of self-motion. We propose a functional sensitivity hypothesis--that self-motion is perceived on the basis of optical information rather than the retinal locus of stimulation, but that central and peripheral vision are differentially sensitive to the information characteristic of each retinal region.     

Extracting thresholds from noisy psychophysical data.

Psychophysical studies with infants or with patients often are unable to use pilot data, training, or large numbers of trials. To evaluate threshold estimates under these conditions, computer simulations of experiments with small numbers of trials were performed by using psychometric functions based on a model of two types of noise: stimulus-related noise (affecting slope) and extraneous noise (affecting upper asymptote). Threshold estimates were biased and imprecise when extraneous noise was high, as were the estimates of extraneous noise. Strategies were developed for rejecting data sets as too noisy for unbiased and precise threshold estimation; these strategies were most successful when extraneous noise was low for most of the data sets. An analysis of 1,026 data sets from visual function tests of infants and toddlers showed that extraneous noise is often considerable, that experimental paradigms can be developed that minimize extraneous noise, and that data analysis that does not consider the effects of extraneous noise may underestimate test-retest reliability and overestimate interocular differences.     

The word-superiority effect does not require a T-scope.

Six experiments examined the possibility of obtaining a word-superiority effect (WSE) without the use of brief stimulus exposures or a poststimulus mask. In each experiment, subjects were presented a stimulus string and two alternative strings that differed by a single letter (Reicher, 1969). The alternatives and stimulus remained in view until subjects responded, and subjects were under no pressure to respond quickly. In Experiments 1-3, the stimuli were presented in very small type so that they were difficult to see. Subjects were significantly more accurate with words than with nonwords, letters embedded among digits, or letters embedded among number signs (#s). In Experiments 4 and 5, the stimuli were embedded in a simultaneously present pattern mask. Subjects were significantly more accurate with words than with single letters by themselves. In the final experiment, the stimuli were presented in a mask with specific spatial frequency characteristics, and performance was significantly better with words than with nonwords. The WSE is a more general phenomenon than previously supposed; it is not limited to a tachistoscopic exposure.     

Amplitude rise time and the perception of the voiceless affricate/fricative distinction.

Variation of amplitude envelope at stimulus onset has been considered to be of primary importance for distinguishing voiceless affricates from fricatives (e.g., [symbol: see text]). In earlier perceptual experiments, however, variation in amplitude rise time was confounded with variation in frication duration. In two experiments, these variables were independently manipulated, and their individual and combined effects for perception of magnitude of [symbol: see text] were examined. Variation in amplitude rise time alone was not sufficient to signal the voiceless affricate/fricative contrast in these experiments, but variation in frication duration alone was sufficient.     

Haptic probing: perceiving the length of a probe and the distance of a surface probed.

Knowing about the properties of objects by wielding them and knowing about the distances of surfaces by striking them with objects as probes are examples of dynamic or effortful touch. Six experiments focused on the invariant mechanical parameters that couple the time-varying states (displacements, velocities) of hand-held rods to the time-varying torques and forces imposed upon them by wielding and probing. There were three major conclusions. First, when a probe is wielded without contact, perceived probe length is a function of the probe's rotational inertia; however, with contact, perceived probe length is affected by the rotational inertia and the distance of the point of contact from the probe's center of percussion. Second, when a surface is struck with a probe, perceived surface distance is affected by the probe's rotational inertia and the angle of inclination of the probe at contact. Third, under seemingly identical conditions of probing, either probe length or surface distance can be perceived selectively without confusion. Results were discussed in terms of haptic information, haptic attention, and the dynamics of probing.     

Quantitative scores of normal and abnormal subjects on Initial-letter Word-association Test.

The quotient of the mean quantitative score on Initial-letter Word-association Test for 193 normal subjects was significantly higher than the quotient of the mean quantitative score of 44 abnormal (psychotic) subjects. This is interpreted as meaning that, in general, the normal subjects have predominantly a positive attitude towards their surrounding world in contradistinction to the abnormal subjects whose attitude was predominantly negative, ambivalent, and repressive. On the other hand, the mean of the quotients of the quantitative scores of the 44 abnormal subjects was higher than the mean of the quotients of the quantitative scores of the normal subjects which suggests increased oral tendencies of the abnormal subjects expressed much as the unwarranted optimism of small children.     

Lingual vibrotactile threshold and suprathreshold responses of normal-speaking black and white young adults.

A paradigm for studying oral sensory tactile function through use of single frequency vibration applied to the dorsal surface of the tongue was administered to a group of 10 young black women and 10 young white normal-speaking women. Analyses showed no differences between groups with regard to lingual vibrotactile threshold of sensitivity or suprathreshold magnitude-estimation scaling responses.     

Response patterns to central auditory tests and the clinical evaluation of Language Fundamentals--Revised: a pilot study.

Tests of central auditory function and measures of receptive and expressive language abilities were administered to 10 children suspected of having central auditory processing disorders. Eight of the 10 subjects displayed expressive language difficulties, suggesting a need to examine more closely the relationship between expressive language and central auditory processing.     

Consistency of use of phonological processes by a sample of educable mentally impaired children.

A group of 10 educable mentally impaired children (M age = 10 yr., 4 mo.) were assessed for use of phonological process under three speaking conditions: production of single words, imitated sentences, and connected speech samples. Only the process of gliding showed significant differences in use among conditions. Results generally indicated that any of those three speaking conditions were viable for eliciting use of phonological processes by such subjects. Results are also discussed in terms of individual differences.     

Auditory subliminal stimulation: a re-examination.

Unconscious or subliminal perception has historically been a thorny issue in psychology. It has been the subject of debate and experimentation since the turn of the century. While psychologists now agree that the phenomenon of visual subliminal stimulation is real, disagreement continues over the effects of such stimulation as well as to its existence in other sensory modalities, notably the auditory. The present paper provides an overview of unresolved issues in auditory subliminal stimulation which explains much of the difficulty that has been encountered in experimental work in this area. A context is proposed for considering the effects of auditory subliminal stimulation and an overview of current investigations in this field is provided.