Even if we focus only on those systems usually associated with touch, we find a number of distinct sensory channels. Some of these have proven incredibly difficult to isolate and study (see e.g., the historical discussion in Gallace and Spence 2014). Indeed, we are just now starting to understand the role and function of the most basic receptor types involved in touch. Another methodological challenge, to which we’ll return, concerns the deep connection between touch and exploratory action (nicely summarized in Jones and Lederman 2006). For touch, many of the historically important empirical investigations have focused on cutaneous touch, especially on mapping the two–point threshold over the extent of the body. This threshold is the minimal distance at which a subject can discriminate two distinct stimuli. Its study requires subjects to remain completely still, while very small probes (like horse hair) are used to generate stimuli. It is much more difficult to measure touch in ecologically salient contexts where there are unconstrained movements using the whole body.