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Tactile distance judgments are prone to a number of physiological and perceptual distortions. One such distortion concerns tactile distances over the wrist being perceptually elongated relative to those within the hand or arm. This has been interpreted as a categorical segmentation effect: The wrist implicitly serves as a partition between two body part categories so that stimuli crossing the wrist appear further apart. The effect could alternatively be explained in terms of specialized acuity at anatomical landmarks (i.e., the wrist). To test these opposing explanations we presented participants with two tactile distances sequentially for comparison (one mediolaterally, across the arm, and the other proximodistally, along the arm). Points-of-Subjective-Equality (DV) were compared on the hand, wrist and arm, on dorsal and ventral surfaces between subjects. If the acuity account were true distances would be elongated in both axes at the wrist. If the categorical segmentation account were true there would be a selective perceived increase of the proximodistal distance at the wrist. A previously reported mediolateral bias was found on all body parts but, consistent with the categorical account, at the wrist the magnitude of the bias was either reduced (dorsally) or not found (ventrally) suggesting a selective proximodistal elongation. We found no evidence of increased acuity in the vicinity of the wrist in this task. Therefore we conclude that the segmentation of the body into discrete parts induces categorical perception of tactile distance.
Abstract
The forced swim test (FST) is a controversial rodent test that has been used for decades, mainly in depression studies. The severity of the procedure makes it ethically questionable and its validity has also been questioned. In this paper we contribute new data to this debate. We identified original research papers related to Major Depressive Disorder (MDD), using rats as models. We compared the citations received by studies that used the FST and by studies that did not, within subsequent human medical papers. The results show that the number of citations received by both groups was very low, but in the papers describing the FST data the median citation number was zero. Citation analysis indicates that the FST is not contributing significantly to the understanding or cure of MDD. We briefly review other approaches that overcome the ethical limitations of the FST, and which might also surpass its efficacy.