Haptic form perception: Relative salience of local and global features

John B. Pierce Laboratory and Yale University, New Haven, Connecticut When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the haptic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.     

Haptic perception of linear extent

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.     

Haptic underestimation of angular extent

To what extent can individuals accurately estimate the angle between two surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a variety of haptic and visual stimuli was examined in a series of nine experiments. Triangular wooden blocks and raised contour outlines comprising different angles and radii of curvature at the apex were used in experiments 1-4 and it was found that subjects consistently underestimated angular extent relative to visual baselines and that the degree of underestimation was inversely related to the actual size of the angle. Angle estimates also increased with increasing radius of curvature when actual angle size was held constant. In contrast, experiments 5-8 showed that subjects did not underestimate angular extent when asked to perform a haptic-visual match to a computerized visual image; this outcome suggests that visual input may 'recalibrate' the haptic system's internal metric for estimating angle. The basis of this cross-modal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addition of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that haptic underestimations of angle occur in a number of different stimulus contexts, but leave open the question of exactly what type of visual information may serve to recalibrate touch in this regard.     

Slippery context effect and critical bands.

This article explored the slippery context effect: When Ss judge the loudness of tones that differ in sound frequency as well as intensity, stimulus context (relative intensity levels at the 2 frequencies) can strongly influence the levels that are judged equally loud. It is shown that the size of the slippery context effect depends on the frequency difference between the tones: Small frequency differences (less than a critical bandwidth) produced essentially no slippery effect; much larger differences produced substantial effects. These results are consistent with a model postulating the existence of a central attentional or preattentive "filter-like" process whose weighting coefficients represent the size of the absolute as opposed to the relative (contextual) component of loudness perception and judgment.     

Unimanual and bimanual tasks and the assessment of handedness in toddlers

The goal of this study was to examine the relations between three different measures of handedness: unimanual reaching, bimanual manipulation and unimanual manipulation. The appropriateness of the task chosen to evaluate handedness was also explored by contrasting different bimanual manipulation tasks for the more or less differentiated (passive\active) roles assigned to each hand. Forty children, between 18 and 36 months of age, were tested in the three conditions. The results show that the degree of bimanual handedness is greater on the bimanual tasks with a strong role differentiation than on the tasks with less differentiation. Bimanual tasks with a strong role differentiation elicited more right‐handedness than unimanual reaching. Among the children who showed handedness in reaching, the correlation between unimanual and bimanual handedness was high, especially for right‐handers. For some tasks, bimanual handedness appeared at the earliest age studied here (18 months), and there was little relationship between bimanual handedness and bimanual skill. In contrast with unimanual reaching, there was no age‐related change in the degree of handedness for either bimanual or unimanual manipulation. There was a bias toward the use of the right hand for unimanual manipulation. It was concluded that grasping is not the best task to employ to look for robust evidence of handedness, and that bimanual tasks offer a better way to estimate handedness in children, as long as the tasks are carefully chosen.     

Anxiety sensitivity and auditory perception of heartbeat

Anxiety sensitivity (AS) is the fear of sensations associated with autonomic arousal. AS has been associated with the development and maintenance of panic disorder. Given that panic patients often rate cardiac symptoms as the most fear-provoking feature of a panic attack, AS individuals may be especially responsive to cardiac stimuli. Consequently, we developed a signal-in-white-noise detection paradigm to examine the strategies that high and low AS individuals use to detect and discriminate normal and abnormal heartbeat sounds. Compared to low AS individuals, high AS individuals demonstrated a greater propensity to report the presence of normal, but not abnormal, heartbeat sounds. High and low AS individuals did not differ in their ability to perceive normal heartbeat sounds against a background of white noise; however, high AS individuals consistently demonstrated lower ability to discriminate abnormal heartbeats from background noise and between abnormal and normal heartbeats. AS was characterized by an elevated false alarm rate across all tasks. These results suggest that heartbeat sounds may be fear-relevant cues for AS individuals, and may affect their attention and perception in tasks involving threat signals.     

Visual marking: dissociating effects of new and old set size

Visual marking makes it possible to ignore old items during search. In a typical study, old items are previewed 1 s before adding an equal number of new items, one of which is the target. Previewing half of the items reduces the search slope relating response time (RT) to overall set size by half. However, this manipulation sometimes only reduces overall RT but not search slope (Experiment 1). By orthogonally varying the numbers of old and new items, Experiment 2 shows that old and new set sizes interactively affect visual marking. Given a constant new set size, the size of the old set has negligible effect on RT. However, increasing the new set size reduces the preview benefit in overall RT. Experiment 3 shows that this reduction may be restricted to paradigms that use temporal segregation cues. Studies should vary old and new set size orthogonally to avoid missing a visual marking effect where one may be present.     

Encoding processes and attentional inhibition in directed forgetting.

Lexical decisions were used to evaluate whether forget (F)-cued prime words affect subsequent encoding of target words relative to remember (R)-cued prime words. In 3 experiments, R-cued primes were better recalled than F-cued primes. Targets that followed F-cued primes were responded to faster than targets that followed R-cued primes in same-case and different-case identity priming. Semantic priming occurred for targets that followed both types of memory-cued primes. However, response times were longer for both related and unrelated targets following R-cued primes relative to F-cued primes. These results indicate that R and F items are processed to similar levels of representation and inhibitory mechanisms do not attenuate encoding of F items. However, there is slower access to working memory for information that follows R-cued items.