Postural stabilization for the control of touching

We attempted to distinguish between task-related (supra-postural) and perceptual influences on postural motions. Two groups of participants had to make very light tactile contact with an adjacent pliable surface while standing with their eyes closed. In the absence of vision, such light touching with a finger is known to reduce sway. For one group, tactile contact with the surface was merely the result of extending the right forearm. For the other group, variability in the point of tactile contact had to be kept to a minimum. Touching reduced postural sway relative to non-touching only for participants in the latter group. The present results, in combination with others addressing similar task differences, question the assumption that information detected haptically and/or visually is used solely to reduce postural fluctuations. It seems that postural fluctuations are modulated to facilitate performance of tasks over and above the task of standing upright and still.     

Perceiving the vertical distances of surfaces by means of a hand-held probe.

Nine experiments were conducted on the haptic capacity of people to perceive the distances of horizontal surfaces solely on the basis of mechanical stimulation resulting from contacting the surfaces with a vertically held rod. Participants touched target surfaces with rods inside a wooden cabinet and reported the perceived surface location with an indicator outside the cabinet. The target surface, rod, and the participant's hand were occluded, and the sound produced in exploration was muffled. Properties of the probe (length, mass, moment of inertia, center of mass, and shape) were manipulated, along with surface distance and the method and angle of probing. Results suggest that for the most common method of probing, namely, tapping, perceived vertical distance is specific to a particular relation among the rotational inertia of the probe, the distance of the point of contact with the surface from the probe's center of percussion, and the inclination at contact of the probe to the surface. They also suggest that the probe length and the distance probed are independently perceivable. The results were discussed in terms of information specificity versus percept-percept coupling and parallels between selective attention in haptic and visual perception.     

On the short-term retention of serial,tactile stimuli

In three experiments using the short-term memory distractor paradigm, Ss attempted to remember which three or four phalanges of the left hand had been stimulated and in what order. The experiments showed that forgetting increased as a function of trials, that such proactive effects could be eliminated by separating the successive trials by several minutes, that both verbal and nonverbal distractor tasks impaired retention, and that forgetting reached a maximum in approximately 6 sec. All of these results concur with those generally obtained for the short-term retention of verbal material. In addition, it was shown that the tactile recall was significantly poorer after an arithmetic distractor task presented visually than after the same task presented aurally. This result suggests an overlap between the mechanisms of tactile retention and the mechanisms of vision.     

Visual storage or visual masking? an analysis of the “retroactive contour enhancement” effect

Standing and Dodwell (1972) reported that a contoured target stimulus which is only poorly identified when exposed briefly against a steady background field can be identified accurately if the field is terminated shortly after target offset. This observation was confirmed and, in addition, it was shown that target identification is enhanced when the field is initiated shortly before target onset. Furthermore, it was demonstrated that a continuous background field is not essential for either effect. It was argued that these “retroactive” and “proactive” enhancements of target identification were due to a complex interaction among forward, backward, and simultaneous masking.     

Short-term retention of tactile stimulation

In three experiments subjects were required to reproduce after varying delays the locus of a tactile stimulation delivered to the upper-side of the arm. During the retention periods subjects either performed a subsidiary, arithmetic task or rested. Recall, as measured by accuracy in reproducing the locus of stimulation, decreased as a function of retention interval, asymptoting after approximately 5 s. Performance was poorer in the subsidiary task condition than in the rest condition; however, the effect of the subsidiary task appeared to be more on subject recall strategies than on rehearsal capacity. No evidence of proactive interference effects was found, and a decay interpretation of forgetting of discrete tactile stimuli in the short-term memory distractor paradigm was favoured.     

Type and number of violations and the grammatical congruency effect in lexical decision

Summary An experiment was conducted in the Serbo-Croatian language in which native speakers/readers made lexical decisions on inflected nouns and legally inflected pseudonouns following inflected possessive pronouns. A possessive pronoun and the noun or pseudonoun that followed it could agree in case, gender, and number (0 violations), disagree in either case or gender or number (1 violation) or disagree simultaneously on two of the three (2 violations). A grammatical congruency effect was observed for both nouns and pseudonouns. Acceptance latencies were shorter and rejection latencies were longer for inflectional agreement than inflectional disagreement. However, for neither nouns nor pseudonouns was the magnitude of the effect influenced by the type or number of violations. The results are discussed in terms of (1) the automaticity of syntactic processes and (2) the properties of a decision making device (specially tailored to rapid lexical evaluations) relative to the properties of the language processor.This research was supported in part by NICHD Grants HD-08495 and HD-01994 to the University of Belgrade and Haskins Laboratories, respectively     

Haptic perception of object distance in a single-strand vibratory web.

Can humans, like other animals, perceive distance by mechanical vibrations transmitted in a solid medium? In seven experiments, subjects perceived the distances from the hand of occluded metal disks attached to a taut nylon strand. Mechanical waves were initiated at the hand by the subject or at the disk by the experimenter. The results of Experiments 1 and 2 showed that perceived distance was linearly dependent on object distance with or without practice. The results of Experiments 3 and 4 revealed an inverse dependency of perceived distance on strand tension. In Experiment 5, a constant difference in perceived distance between vertical and horizontal strand manipulations was found. The results of Experiments 6 and 7 showed that distance was perceptible when the mechanical wave was not initiated by the subject. The informational basis for this haptic spatial ability was sought in the dynamics expressed by the one-dimensional wave equation, specifically, in the constants relating strand forces to strand motions.