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...