Primacy of dimensions in vibrotactile perception: An evaluation of early holistic models

Early holistic models of perception presume that stimuli composed of interacting dimensions can be experienced initially as undifferentiated. This view, formalized through recourse to a Euclidean geometry of perceptual space, predicts that the orientation of axes used to create stimulus sets is unimportant to performance in speeded classification. We tested this idea by using the interacting vibrotactile dimensions of pitch and loudness. Despite perceivers’ relatively poor experience with these dimensions, we showed that the orientation corresponding to pitch and loudness was unique in vibrotactile perceptual space; subjects classified stimuli more efficiently at this orientation than at other orientations. Certain holistic models also claim that when stimulus differences are small, perceivers can recognize change without distinguishing the kind of change. We tested this idea by using a signal detection analysis of unspeededsame—different decisions. We found that subjects’ ability to notice the kind of change equaled their ability to notice the change alone. In view of these results, which indicate that pitch and loudness are primary in vibrotactile perception, we detail a new conception of dimensional interaction.     

Interpolation in structure from motion

We investigated surface interpolation in displays of structure from motion (SFM). To do so, we introduced a new method for measuring surface perception in dynamic displays—theSFM probe. An SFM probe is a dot that moves rigidly with the dots on a simulated surface, and whose distance from that surface can be adjusted with a joystick or similar control. The displays we studied were random-dot cylinders containing a vertical strip devoid of feature points (thegap). Subjects adjusted an SFM probe, presented in the gap, until the probe dot appeared to be on the surface. Variability in probe-dot placement decreased with increasing texture density on the cylinder and increased with increasing gap width. Subjects showed a consistent bias to place the probe dot outside the cylinder. This bias increased with increasing texture density for the SFM displays. (The opposite bias was found in a static two-dimensional interpolation task with an arc whose curvature matched that of the cylinder: Subjects placed the probe dot inside the arc.) This outside bias is inconsistent with several theoretical approaches to surface interpolation.     

Three-space inference from two-space stimulation

Oblique contours sloping at 30° with respect to the horizontal were presented alone, in combination to form chevrons, or with a vertical line to form arrowhead or Y patterns; they were projected onto a screen in the frontal parallel plane and viewed from positions that gave viewing angles of 90° (normal to the screen’s surface), 53°, or 34°. The perceived orientation of the contours, as assessed by a movable arm that the subjects set to be parallel to the obliques, changed monotonically as a function of viewing angle. The change was as great for single obliques as for combinations of obliques within the chevron, arrowhead, and Y patterns. The results of Experiment 1 were extended in Experiment 2, in which obliques at 30° and 50° with respect to the horizontal were presented singly or in combination as chevron patterns. It is argued that the results of both experiments indicate that single two-space oblique lines are immediately interpreted as lying in three-space and that the changes in perceived orientation are a consequence of this perceptual inference.     

Neighborhood frequency effects and letter visibility in visual word recognition

Two experiments are described that measured lexical decision latencies and errors to five-letter French words with a single higher frequency orthographic neighbor and control words with no higher frequency neighbors. The higher frequency neighbor differed from the stimulus word by either the second letter (e.g.,astre-autre) or the fourth letter (chope-chose). Neighborhood frequency effects were found to interact with this factor, and significant interference was observed only tochope-type words. The effects of neighborhood frequency were also found to interact with the position of initial fixation in the stimulus word (either the second letter or the fourth letter). Interference was greatly reduced when the initial fixation was on the critical disambiguating letter (i.e., the letterp inchope). Moreover, word recognition was improved when subjects initially fixated the second letter relative to when they initially fixated the fourth letter of a five-letter word, but this second-letter advantage practically disappeared when the stimulus differed from a more frequent word by its fourth letter. The results are interpreted in terms of the interaction between visual and lexical factors in visual word recognition.     

Visually controlled matching of pattern movement

Utrecht Biophysics Research Institute, Rijksuniversiteit Utrecht, Utrecht, The Netherlands Subjects were asked to match the speeds of two moving random-dot patterns seen through circular apertures. The speed of one pattern that moved horizontally toward the right of a computer screen changed continuously. The speed of this pattern represented the target. It was to be matched with the speed of the second pattern, which moved in the opposite direction. The subject controlled the speed of the second pattern by means of an isometric joystick. The distance between the apertures on the screen as well as the subject’s distance from the screen served as experimental parameters. In this way, the effects of both spatialand temporal transients of pattern speed on human tracking performance were studied. To avoid anticipation by the subject, the amplitude and the frequency of the target pattern speed changed pseudorandomly. The accuracy with which the subject performed the matching task was influenced by the mean pattern speed and the parameters of the visual field. Within lower velocity ranges, the subject’s sensitivity to the instantaneous speed differences varied according to Weber’s law. The cross-correlation of the velocity time courses decreased when the mean speed of the target pattern was increased. Two stimulus parameters had a strong influence on the modulation of the correlation value: (1) the angular size of the stimulus on the retina and (2) the retinal eccentricity of the stimulus.     

Increasing the intelligibility of speech through multiple phonemic restorations

Outside of the laboratory, listening conditions are often less than ideal, and when attending to sounds from a particular source, portions are often obliterated by extraneous noises. However, listeners possess rather elegant reconstructive mechanisms. Restoration can be complete, so that missing segments are indistinguishable from those actually present and the listener is unaware that the signal is fragmented. This phenomenon, called temporal induction (TI), has been studied extensively with nonverbal signals and to a lesser extent with speech. Earlier studies have demonstrated that TI can produce illusory continuity spanning gaps of a few hundred milliseconds when portions of a signal are replaced by a louder sound capable of masking the signal were it actually present. The present study employed various types of speech signals with periodic gaps and measured the effects upon intelligibility produced by filling these gaps with noises. Enhancement of intelligibility through multiple phonemic restoration occurred when the acoustic requirements for TI were met and when sufficient contextual information was available in the remaining speech fragments. It appears that phonemic restoration is a specialized form of TI that uses linguistic skills for the reconstruction of obliterated speech.     

Neonatal imitation of tongue protrusion and mouth opening: Methodological aspects and evidence of early individual differences

The present work examines imitation of mouth opening and tongue protrusion in 32 full-term infants at three different occasions: When the infants are two to three days, three weeks, and three months old. The analysis focuses (1) on individual differences in imitative behaviour and (2) on how to operationalize the infants' responses. The overall group analysis revealed that imitation of tongue protrusion was statistically significant for both two- to three-day-old and three-week-old infants but not when the children had become three months old. No statistically significant effect was observed for imitation of mouth opening. Two different imitation indexes were constructed in order to assess individual differences in early imitative behaviour. Results show that short-term stability in imitative tendencies exists between the first and second observation. The results further reveal that methodological factors must be seriously considered when studying neonatal imitation: the overall imitation found for tongue protrusion is demonstrated to be dependent on how the infants' responses are coded.     

Alternating least squares algorithms for simultaneous components analysis with equal component weight matrices in two or more populations

Millsap and Meredith (1988) have developed a generalization of principal components analysis for the simultaneous analysis of a number of variables observed in several populations or on several occasions. The algorithm they provide has some disadvantages. The present paper offers two alternating least squares algorithms for their method, suitable for small and large data sets, respectively. Lower and upper bounds are given for the loss function to be minimized in the Millsap and Meredith method. These can serve to indicate whether or not a global optimum for the simultaneous components analysis problem has been attained.Financial support by the Netherlands organization for scientific research (NWO) is gratefully acknowledged.     

Minimizing the number of observations: A generalization of the spearman-brown formula

A new method for determining the minimum number of observations per subject needed to achieve a specific generalizability coefficient is presented. This method, which consists of a branch-and-bound algorithm, allows for the employment of constraints specified by the investigator.     

Sex stereotypes in Norway revisited: 1977–87

In 1977 sex-trait stereotypes in Norway were measured at the young adult level and at the level of five-year-olds. At the young adult level the Adjective Check List was used, and the results were analysed according to an affective meaning scoring system, and a scoring system based on Transactional Analysis. The instrument used for children was a picture-story technique (Sex Stereotype Measure II). Persistence and change in sex-trait stereotypes were examined by replicating the study in 1987. Quantitatively, young adults' sex-trait stereotypes seemed to have changed little during the last decade, but qualitative analyses indicated that stereotypes have changed in the direction of greater favourability, activity and strength towards women and in the reverse direction towards men. The children in the 1987 sample expressed less stereotype knowledge than children in the 1977 sample concerning traits which traditionally have been ascribed to men.