Manual discrimination and identification of length by the finger-span method

Self Cite

191

114

In these experiments, two plates were grasped between the thumb and-forefinger and-squeezed together along a linear track. An electromechanical system presented a constant resistance force during the squeeze up to a predetermined location on the track, whereupon the force effectively went to infinity (simulating a wall) or to zero (simulating a cliff). The task of the subject was to discriminate between two alternative levels of the constant resistanceforce~areference level and a reference-plus-increment level). Results of these experiments indicate a just noticeable difference of roughly 7% of the reference force using a one-interval paradigm with trial-by-trial feedback over the ranges 2.5 F 0 10.0newtons, 5 D 30 mm, 45 S 125 mm, and 25s V 160 mmlsec, where F 0 is the reference force, D is the distance squeezed, S is the initial fingerspan, and V is the mean velocity of the squeeze. These results, based on tests with 5 subjects, are consistent with a wide range of previous results, some of which are associated with other body surfaces and muscle systems and many of which were obtained with different psychophysical methods. This is the second in a series of papers concerned with the manual perception of objects, and, more specifically, with the ability to distinguish between different objects manually (i.e., with manual resolution). In the first paper, we reported the results of a variety of experiments in which the subject was required to discriminate or identify object length by means of the finger-span method (Durlach et al., 1989). In these experiments, a rigid object was grasped between the terminal pads of the thumb and forefinger, and object length was estimated by sensing the differential position of these pads. In the present series of experiments, an object was again grasped between the terminal pads of the thumb and forefinger; in this case, however, the object was not rigid, and the task was to squeeze the object and estimate the resistance force. The experimental apparatus was designed in such a way that the force was constant over the displacement resulting from the squeeze, the force was varied between squeezes, and the task was to discriminate between two alternative levels of the force. In the length-resolution task, the response is derived from estimates of finger position. In the current task, the response is derived from estimates of finger force. In both cases, perceptual cues This work wassupported by ONR Grants N00014-88-K-0338, N00014-89-J-3247, and N00014-90-J-1935, NJ}l Grant 2-R01-DC00126-11, Fairchild foundation funds awarded to X. D. Pang, and a Chu Fellowship to H. Z. Tan. The support and contributions of John Hollerbach at all levels of this work are greatly appreciated. We would also like to thank Bill Rabinowitz for his help with the instrumentation and other aspects ofthe work. We appreciate the contributions of Younes Borki, Lorraine Delhorne, Mary Hou, and Mandayain Srinivasan. are available from both the cutaneous sensory system and the kinesthetic/proprioceptive sensory sys...

mentioning

confidence: 99%

Manual discrimination of force using active finger motion

Pang

Tan

Durlach

1991

Self Cite

191

114

“…Furthermore, the discrimination thresholds increased by a factor ofabout two under conditions ofvarying contact lengths. Durlach et al (1989) and Tan, Pang, and Durlach (1992) investigated haptic length perception and did not find systematic oyerestimations or underestimations for length perception by means ofthe finger-span method. However, it is quite difficult to extrapolate their results to ours, because the manner in which the stimuli were touched and their experimental task were different.…”

mentioning

confidence: 99%

Similar mechanisms underlie curvature comparison by static and dynamic touch

Pont

Kappers

Koenderink

1999

103

In four experiments, we tested whether haptic comparison of curvature ranging from -41m to +41m is qualitatively the same for static and for dynamic touch. In Experiments 1 and 3, we tested whether static and dynamic curvature discrimination are based on height differences, attitude (slope) differences, curvature differences, or a combination of these geometrical variables. It was found that both static and dynamic haptic curvature discrimination are based on attitude differences. In Experiments 2 and 4, we tested whether this mechanism leads to errors in the comparison of stimuli with different lengths for static and dynamic touch, respectively. If the judgments are based on attitude differences, subjects will make systematic errors in these comparisons. In both experiments, we found that subjects compared the curvatures of strips of the same length veridically, whereas they made systematic errors if they were required to compare the curvatures of strips of different lengths. Longer stimuli were judged to be more curved than shorter stimuli with the same curvature. Weconclude that similar mechanisms underlie static and dynamic haptic curvature comparison. Moreover, additional data comparison showed that static and dynamic curvature comparison is not only qualitatively, but also quantitatively similar.When we touch an object, we get an impression of, for instance, its texture, size, temperature, and shape. The geometrical correlate of the shape of smooth objects is curvature. So, an understanding of curvature perception contributes to the comprehension of the mechanism of shape perception. In this paper, we focus on the manner in which haptic curvature discrimination takes place in the cases of static and dynamic touch. It is evident that the results are interesting in themselves, but, in addition, we are able to compare the two cases in order to investigate whether dynamic curvature comparison follows the same principles as static curvature comparison.In earlier investigations (Pont, Kappers, & Koenderink, 1995, we tested static haptic discrimination of curved strips for different placements relative to the hand and for different lengths ofthe stimuli. The strips had a length of 8 or 20 em, a width of 2 ern, and a curvature ranging from -1.8/m to +1.8/m (the curvature is the reciprocal ofthe radius of curvature, and vice versa). Performance in the conditions in which the stimuli were touched with the palmar side ofthe hand was found to depend priWe are grateful to the Netherlands Organization for Scientific Research (NWO) for funding this project. We thank Heino Blanckaert, Jasper Berben, Ronald Burger, Norbert van Woerkom, Michiel Bijlsma, Femius Koenderink, and lnge Lichtenegger for acting as observers and Sheila McNab, whose critical comments have improved the language style of the manuscript. Special thanks go to Hans Kolijn for his technical help. Correspondence concerning this article should be sent to S. C. Pont, Utrecht University, Helmholtz Instituut, Princetonplein 5, 3584 CC Utrecht, The Netherlands ...

“…This is the third in a series ofpapers concerned with how individual physical properties of objects are perceived. In the first paper of this series (Durlach et al, 1989), we reported the results ofa variety ofexperiments in which the subject was required to discriminate or identify object length (related to the variable x) by means of the fingerspan method. The just noticeable difference (JND) in length measured in discrimination experiments was roughly 1 rom for reference lengths of 10-20 rom, and increased to roughly 2.2 rom for a reference length of80 rom.…”

mentioning

confidence: 99%

Manual discrimination of compliance using active pinch grasp: The roles of force and work cues

Tan

Durlach

Beauregard

et al. 1995

184

121

In these experiments, two plates were grasped between the thumb and the index finger and squeezed together along a linear track The force resisting the squeeze, produced by an electromechanical system under computer control, was programmed to be either constant (in the case of the force discrimination experiments) or linearly increasing (in the case of the compliance discrimination experiments) over the squeezing displacement, After completing a set of basic psychophysical experiments on compliance resolution (Experiment I), we performed further experiments to investigate whether work and/or terminal-force cues played a role in compliance discrimination, In Experiment 2, compliance and force discrimination experiments were conducted with a roving-displacement paradigm to dissociate work cues (and terminal-force cues for the compliance experiments) from compliance and force cues, respectively. The effect of trial-by-trial feedback on response strategy was also investigated. In Experiment 3, compliance discrimination experiments were conducted with work cues totally eliminated and terminal-force cues greatly reduced. Our results suggest that people tend to use mechanical work and force cues for compliance discrimination, When work and terminal-force cues were dissociated from compliance cues, compliance resolution was poor (22%) relative to force and length resolution. When work cues were totally eliminated, performance could be predicted from terminal-force cues. A parsimonious description of all data from the compliance experiments is that subjects discriminated compliance on the basis ofterminal force.To a first approximation, the mechanical behavior of all deformable solid objects can be expressed as! = F' . + Kx + Bx + mx, which represents the relationship between the total force (f) applied on the object and the corresponding displacement (x), velocity (x), and acceleration (i); the frictional force (F'.), linear stiffness (K), viscosity (B), and mass (M) are the physical parameters that distinguish one object from another (we use lowercase letters for variables and uppercase for parameters). It is our goal to study manual resolution ofall these physical variables and parameters and to provide basic psychophysical information that can be used to (1) advance our understanding of manual perception of object properties, (2) guide the development of design specifications for haptic interfaces that not only sense position and force commands from the human operator but also display such information to the operator in teleoperation and virtual environment systems (see, e.g., the recently published book on systems of this type edited by Durlach & Mavor, 1994), and (3) improve the design of autonomous robots that must make use of manual sensing and manipulation. This is the third in a series ofpapers concerned with how individual physical properties of objects are perceived. In the first paper of this series (Durlach et al., 1989), we reported the results ofa variety ofexperiments in which the subject was required t...