Curvature affects haptic length perception

One possible way of haptically perceiving length is to trace a path with one’s index finger and estimate the distance traversed. Here, we present an experiment in which observers judge the lengths of paths across cylindrically curved surfaces. We found that convex and concave surfaces had qualitatively different effects: convex lengths were overestimated, whereas concave lengths were underestimated. In addition, we observed that the index finger moved more slowly across the convex surface than across the concave one. As a result, movement times for convex lengths were longer. The considerable correlation between movement times and length estimates suggests that observers take the duration of movement as their primary measure of perceived length, but disregard movement speeds. Several mechanisms that could underlie observers’ failure to account for speed differences are considered.     

Tactile-kinesthetic space estimation: The influence of gravity

Summary The capacity to estimate the orientation of an object with respect to gravity was investigated by having Ss rotate a tactile-kinesthetically (tk) perceived bar (under exclusion of all visual cues) to the subjective horizontal. The 1st experiment was conducted to compare tk judgements with the visual judgements obtained by Udo de Haes (1970a,b) about an object's orientation in order to study the underlying mechanism, particularly to show possible vestibular influence, if any. For this purpose Ss were required to orient the tk-perceived bar while subjected to changes in both the magnitude (by centrifugation) and the direction (by tilting the body) of the gravitational force. Great variability of S's adjustments in the nearly inverted body positions (120°, 150°), indicating a low stability of spatial orientation in this range, was common to both tk and visual estimations. The relationship between body tilt and the corresponding judgement about the object's orientation, was however different for the two systems: No linear proportionality to the shear force in the utricles, as was established earlier in the visual experiments of Udo de Haes, was found in the tk settings. Vestibular influence was further studied in the 2nd experiment by comparing bar adjustments of the right hand with those of the left hand. Increasing angles of body tilt produced similar results in the responses of both hands although shifted differently from the true values. Standard deviations of left-hand settings were lower than those of right-hand ones. Reactions to increased gravity differed between hands. In the 3rd experiment the hand-weight alone, not the whole gravitational force, was increased. A direct effect of gravity on the adjusting hand was found. It was concluded that 1) the underlying mechanisms for tk and visual space estimations with respect to gravity are different; 2) with the given tk stimulation vestibular influence is not recognizable; 3) muscle receptors are probably significant, in addition to joint receptors, for this mode of space estimation, and 4) both arms may represent a system to perceive the direction of gravity independent of each other and of the labyrinth.     

Microgenesis of the length perception of paired lines

The changes in perception associated with exposure time are probably continuous in the microgenetic process, as is demonstrated by such phenomena as intensity change in illusions, adaptation and normalization, practice effect, aftereffects, etc. The simultaneous contrast and assimilation in the perception of length of paired lines were measured by controlling the exposure duration or repetition. In the tachistoscopic experiment, the greatest contrast appeared at an early stage of microgenesis. In the repeated presentation experiment, the perception changed from contrast to assimilation on the expanded stage of microgenesis. These changes in perception are assumed to be the results of the differentiation of set that progresses in the microgenetic process. In the fixed-set experiment, the differentiation of set was reflected in the intensity of the aftereffect. The changes in the aftereffect and the transformation into the assimilation coincided with each other when the exposure time was varied. An expansion of the conception of perceptual microgenesis to a wider range of perceptual variability is accordingly proposed.     

Exploration styles modulate length perception through dynamic touch

One of the most surprising capacities of the haptic system is the ability to estimate different properties of objects, like weight or length, through invariants of rotational mechanics that are accessible via the proprioceptive system. This field of research is called Dynamic Touch. In its classical experimental paradigm, the participant firmly grasps a rod that can be wielded but not seen, and he or she tries to match the hand-held rod's length using another rod that can be seen but not wielded. In the experiment reported here, we focus on the role of the exploratory behavior, restricting the wielding in six conditions that vary both the amplitude and the frequency of movements. Increments in the speed of the movement are shown to increase the accuracy in the haptic estimation. It is argued that these results support the moment of inertia as the best informational candidate, given that it is an invariant property that only emerges when rotational torques are applied. Alternative candidates such as static moment or mass are discarded because they do not depend on differential movements.     

Transfer of calibration in length perception by dynamic touch

Earlier studies suggested that the calibration of actions is functionally, rather than anatomically, specific; thus, calibration of an action ought to transfer to actions that serve the same goal (Rieser, Pick, Ashmead, & Garing, 1995). In the present study, we investigated whether the calibration of perception also follows a functional organization: If one means of detecting an information variable is recalibrated, are other means of detection recalibrated as well? In two experiments, visual feedback was used to recalibrate perceived length of a rod wielded by the right hand; the recalibration was found to transfer to length perception with the left hand. This implies that calibration in perception is organized functionally rather than anatomically, and supports the general view that calibration applies to functional systems.     

The perception of length on curved and flat surfaces

In three experiments, observers judged the apparent extents of spatial intervals along the surface of a curved cylinder or a flat plane that was binocularly viewed in a natural, indoor environment. The observers' judgments of surface lengths were precise and reliable but were also inaccurate and subject to relatively large constant errors. These distortions differed among the observers, but they tended to perceive lengths oriented along the curved dimension of the cylinder as being longer than physically equivalent lengths in the noncurved dimension. This phenomenon did not occur when the observers judged curved and noncurved paths on the flat surface. In addition, some observers' judgments of length were affected by changes in the distance to the cylinder, whereas others were affected by the cylinder's orientation in space. These results demonstrate that the perception of length on surfaces is highly dependent on the particular context in which the length occurs.     

The visual perception of length along intrinsically curved surfaces

The ability of observers to perceive three-dimensional (3-D) distances or lengths along intrinsically curved surfaces was investigated in three experiments. Three physically curved surfaces were used: convex and/or concave hemispheres (Experiments 1 and 3) and a hyperbolic paraboloid (Experiment 2). The first two experiments employed a visual length-matching task, but in the final experiment the observers estimated the surface lengths motorically by varying the separation between their two index fingers. In general, the observers' judgments of surface length in both tasks (perceptual vs. motoric matching) were very precise but were not necessarily accurate. Large individual differences (overestimation, underestimation, etc.) in the perception of length occurred. There were also significant effects of viewing distance, type of surface, and orientation of the spatial intervals on the observers' judgments of surface length. The individual differences and failures of perceptual constancy that were obtained indicate that there is no single relationship between physical and perceived distances on 3-D surfaces that is consistent across observers.     

The situational effects on haptic perception of rod length

Three experiments were conducted to investigate situational effects (manipulation, range, and prior experience) on the haptic perception of rod length. Each rod was held between its two ends with one hand. In Experiment 1, 32 participants judged length of rods using different manipulations. Perceived lengths were found to be dependent on manner of manipulation and not necessarily equal to actual lengths. Different parameters were detected in different manipulations. In Experiment 2, 8 participants judged rod lengths by wielding rods of two ranges: long and short. Perceived length was found to be affected by the range of rods evaluated successively in a single set. In Experiment 3, 9 participants judged rod lengths after an experience of handling dense or light rods. Perceived length was found to be affected by prior experience. Results are discussed in terms of how rod lengths can be perceived accurately by haptic modality without involving direct perception.     

Inertia tensor and weight-percept models of length perception by static holding

S. J. Lederman, S. R. Ganeshan, and R. E. Ellis (1996) reported an experiment demonstrating that for occluded rods of equal mass and length but different diameters length perception by static holding was larger for rods of smaller diameter. They concluded that participants inferred length from illusory weight percepts. However, rods of equal mass and length that differ in diameter also differ in the eigenvalues of their respective inertia tensors. In the present experiments, the authors manipulated the diameters (Experiment 1) and the inertial eigenvalues (Experiments 4 and 5) of statically held objects. As has been shown with wielded objects, perceived length was a function of the eigenvalues. Additional experiments failed to confirm the expectation from the weight-percept model that perceived length maps to the estimated weight (Experiments 2 and 3). Physical quantities, not psychological quantities, seem to explain length perception by static holding.     

Attention and perception, memory, and judgment of line length

The literature reports that focused attention alters perceived length of lines. Some tests of this attentional effect require that subjects compare line lengths. This note shows that conceptual confusions inherent in this comparison make the tests invalid.     

The effect of density and diameter on haptic perception of rod length

Three experiments on the effect of density and diameter on haptic perception of rod length are reported. In Experiment 1, the subjects wielded visually occluded rods of different densities. Perceived length was found to be affected by the density of the rod regardless of the actual length. In Experiment 2, three aluminum rods of different lengths with handles of four different diameters were wielded. Perceived length of the rod was found to be shorter as the diameter of the handle with which it was wielded increased. A diameter—length illusion was thereby produced. In Experiment 3, visually occluded rods of different diameters but of the same moment of inertia about thex-axis were wielded with the right hand, and tubes of different diameters were felt with the left hand. The subjects were instructed that their right hand was grasping a handle, and that the actual diameter of the rod could be felt with the left hand. Rods were perceived to be shorter if a larger diameter was felt with the left hand. The results showed that perceived length is not just a function of actual rod length, and that it is not accounted for by inertia only. The results are further discussed in terms of the nature of invariants and the effect of knowledge on perception.     

Application of signal detection theory to perception of differences in line length

This paper is an attempt to specify the equinormal model for application to different tasks which are currently used in psychophysics (i.e. phenomenal report, detection, and 2AFC). The same set of stimuli (pairs of horizontal colinear lines) is presented in procedures which differ by the task, the probability of the signal, and the succession of the stimuli of the set. This approach leads to the specification of the sensorial and the decisional aspects of the model.The data indicate that (1) the sensitivity index d' to differences in line length is the same function of the physical stimulus independently of paradigm, as far as the same task is concerned. However, and according to the predictions, its value becomes larger by a factor of 2 in a two alternative forced choice task; (2) d' increases with stimulus exposure time; (3) latency of responses generally decreases with increasing d', and are dissimilar for correct and incorrect responses; (4) when the temporal succession of the stimuli is random the subject's criterion, x_c, is not chosen to optimize the percentage correct, which would require a dependance of criterion upon stimulus amplitude and prior probabilities.     

The role of effective lever length in the perception of lifted weights

Objects are lifted through a system of body levers and, since the force required to lift objects decreases as the effective lever length is shortened, it was hypothesized that the perceived heaviness of objects would be less when they were lifted with the elbow bent than with it extended. Cans lifted from greater initial angles were consistently judged to be lighter by blindfolded Ss.     

Detection of invariants by haptic touch across age groups: rod length perception

This study examined the development in the detection of maximum eigenvalues and static moment as invariants, through a task of perceiving rod length without visual information by haptic touch. 34 participants ages 6 to 83 years participated in the experiment. Their exploratory behavior and perceptions of rod length were analyzed by age group (Children: 6 to 12 years old; Young Adult: 21 to 25 years old; Middle Age: 31 to 56 years old; and Older: 65 to 83 years old). A behavior analysis indicated that use of vertical swinging increased for the Young Adult group and decreased with age for the Older group, whereas Children frequently held the rod without wielding. Analysis showed that, by age, differences in coefficients on the maximum eigenvalue and static moment were parallel with an exploratory behavioral change. Finally, the effect of different exploratory behaviors on length perception was discussed.     

Changing grasp position on a wielded object provides self-training for the perception of length

Calibration of perception to environmental properties typically requires experiences in addition to the perceptual task, such as feedback about performance. Recently, it has been shown that such experiences need not come from an external source or from a different perceptual modality. Rather, in some cases, a given perceptual modality can train itself. In this study, we sought to expand on the range of experiences in which this can occur for perception of the length of a wielded occluded object. Specifically, in two experiments, we investigated whether the act of perceiving the length of a wielded object from a given grasp position could recalibrate the perception of length from a different grasp position. In both experiments, three groups of participants perceived the lengths of wielded rods in a pretest, practice, and a posttest. The practice included either (a) experimenter feedback, (b) changing the grasp position on the object (and again attempting to perceive length), or (c) no additional experiences. In Experiment 1, participants changed their grasp position from the middle to the end of each rod, and in Experiment 2, they did so from the end to the middle of each rod. In both experiments, the results showed that perceiving length from a different grasp position can recalibrate (i.e., provide self-training for) the perception of length.     

Inertial eigenvalues, rod density, and rod diameter in length perception by dynamic touch

Four experiments addressed the relevance of the eigenvaluesI _k of the inertia tensor for perceiving length by dynamic touch. Experiments 1–2 focused on the consequences of limiting variation in the minimum eigenvalueI ₃. Both revealed that perceived length is a function ofI _k . Whether the contribution ofI ₃ is detected, however, depends on the range of values that characterize a particular object set. Experiments 3–4 considered the relationship between an independent index of a rod’s diameter, which does not affectI _k , and actual manipulation of a rod’s diameter, which does affectI _k . Whereas the former appeared as satisfaction of implicit instructions to alter reports of perceived length, the latter entailed actual differences in perceived length in accordance withI _k . Results are discussed with respect to the links among actual length, perceived length, andI _k , as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.     

Context effects in visual length perception: role of ocular,retinal, and spatial location

In three experiments, we examined the transfer of orientation-contingent context effects between the eyes and across portions of the retina with or without variation in external spatial location. Previous research had shown that vertical lines are judged long, relative to horizontal lines, when the stimulus set comprises relatively long horizontals and short verticals (Contextual Condition B), as compared with the reverse when the stimulus set comprises relatively short horizontals and long verticals (Contextual Condition A). Consequently, the contextual set of stimuli influences the magnitude of the horizontal-vertical illusion (HVI), decreasing its size under Contextual Condition A and increasing its size under Contextual Condition B. Experiment 1 showed that exposing one eye to different stimulus contexts modulated the size of the HVI at the exposed eye but had little or no effect at the other eye. Experiments 2 and 3 showed that the effect of the contextual sets generalized poorly across adjacent portions of the retina but transferred almost perfectly across different locations in external space when retinal location was constant. Thus, orientation-contingent context effects in visual length perception appear to be specific to the eye and to the region of the retina stimulated, suggesting that these effects reflect relatively early and local changes in sensitivity, rather than relatively late and general shifts in response criteria.     

How mechanical context and feedback jointly determine the use of mechanical variables in length perception by dynamic touch

Earlier studies have revealed that both mechanical context and feedback determine what mechanical invariant is used to perceive length by dynamic touch. In the present article, the authors examined how these two factors jointly constrain the informational variable that is relied upon. Participants were to judge length while wielding a rod or while holding it stationary. In two experiments, it was tested whether perceptual learning effects in the wielding condition transferred to the holding condition and vice versa. There was an asymmetry in transfer across mechanical conditions: Improvements in the holding context transferred to the wielding condition, but not vice versa. Examining the individuals’ exploitation of mechanical variables, we found that, after feedback, participants changed in information usage in both mechanical conditions. For many participants, these changes were not confined to the mechanical context in which the feedback was provided. Indeed, feedback in one mechanical context brought about changes in information usage that often manifested themselves in the other mechanical condition. The authors explore the implications of these findings for research on perceptual learning in dynamic touch and the salience hypothesis.     

Children's intuitive sense of number develops independently of their perception of area,density, length,and time

Young children can quickly and intuitively represent the number of objects in a visual scene through the Approximate Number System (ANS). The precision of the ANS – indexed as the most difficult ratio of two numbers that children can reliably discriminate – is well known to improve with development: whereas infants require relatively large ratios to discriminate number, children can discriminate finer and finer changes in number between toddlerhood and early adulthood. Which factors drive the developmental improvements in ANS precision? Here, we investigate the influence of four non‐numeric dimensions – area, density, line length, and time – on ANS development, exploring the degree to which the ANS develops independently from these other dimensions, from inhibitory control, and from domain‐general factors such as attention and working memory that are shared between these tasks. A sample of 185 children between the ages of 2 and 12 years completed five discrimination tasks: approximate number, area, density, length, and time. We report three main findings. First, logistic growth models applied to both accuracy and Weber fractions (w; an index of ANS precision) across age reveal distinct developmental trajectories across the five dimensions: while area and length develop by adolescence, time and density do not develop fully until early adulthood, with ANS precision developing at an intermediate rate. Second, we find that ANS precision develops independently of the other four dimensions, which in turn develop independently of the ANS. Third, we find that ANS precision also develops independently from individual differences in inhibitory control (indexed as the difference in accuracy and w between Congruent and Incongruent ANS trials). Together, these results are the first to provide evidence for domain‐specific improvements in ANS precision, and place children's maturing perception of number, space, and time into a broader developmental context.