1 Introduction In the history of the study of tactile perception, a recurrent problem has been that of the relative influences of space and time on the localization of stimuli on the skin. With moving or changing stimuli, it is difficult to identify or define either a spatial or a temporal extent without acknowledging the influence of the other dimension in the judgment. For example, classical measurements of the two-point limen may be affected by whether the two points are presented simultaneously or successively (Dellon 1981; Johnson et al 1993; Jones 1956). The error of localization (measuring whether the same point was touched twice) may similarly be affected by the time between stimuli. In fact, in vision, audition, and the cutaneous senses, illusions of many types have their bases in such spatiotemporal interactions. The Phi phenomenon (or apparent movement, Graham 1965; Sherrick and Rogers 1966), the Tau effect (Helson and King 1931), and sensory saltation (Geldard 1975) are only three such illusions that have been studied in one or more sensory modalities (eg Collyer 1976; Shore et al 1998). In this paper judgments of distance between two brief tactile stimuli are discussed, particularly as such judgments are influenced by space and time. The importance of the ability to make such distance judgments and discriminations can be seen in tasks ranging from the apprehension of objects in the everyday exploration of our environ- ment, to the use of sophisticated aids that provide vibrotactile patterns to be read by blind persons in mechanized Braille or text devices, or tactile patterns of transformed speech signals to be decoded in aids to lipreading for deaf persons. Although it may appear to be a relatively elementary task, the judgment of tactile distance has a long history of investigation. As long ago as 1826, Ernst Weber began his book, De Subtilitate Tactus, with a discussion of the differences in tactile sensitivity across different parts of the body (1826/1978, page 19). His first proposition was that not all parts of the body were ``equally sensitive to the spatial separation of two simultaneous points of contact'' ödescribing the variation in what has come to be known as the two-point threshold. There is an associated measure when the stimuli are separated by a much longer temporal interval: the error of localization. In this case, The perception of tactile distance: Influences of body site, space, and time Perception, 1999, volume 28, pages 851 ^ 875 Roger W Cholewiak Department of Psychology, Green Hall, Princeton University, Princeton, NJ 08544-1010, USA; e-mail: rcholewi@Princeton.edu Received 19 October 1998, in revised form 8 April 1999 Abstract. Vibrotactile prostheses for deaf or blind persons have been applied to any number of different locations on the body, including the finger, wrist, forearm, abdomen, back, and nape of the neck. The discriminability of patterns presented by such devices can be affected by the acuity of the site of application and the resolution of the display. In addition, the mutual influen- ces among stimuli close together in both space and time can affect percepts within a broad range of parameters. For example, consideration must be given to a variety of tactile illusions often associated with the spatial separations and the range of temporal intervals typically used in cutaneous communication displays. Experiments are reported in which magnitude estimates and cross-modality matches of perceived extent produced by pairs of vibrotactile taps presented to separate loci were obtained on three different body sites. Perceived distance was directly related both to the timing between the taps and to their physical separation. The findings show a consistent relationship to cortical magnification across body sites. DOI:10.1068/p2873