In our first experiment (Figure 1), we found that neurons tended to demonstrate a region of peak response with gradual reduction of the response as a function of distance with the possibility for representations at larger distances. To better understand the local parametric structure of tactile receptive fields, we performed a second experiment that tested collinear sites at finer spatial resolution. (A) We performed a task variant aimed at estimating the size of neuronal receptive fields to actual touch ('Materials and methods: Receptive field size'). In this variant, we tested actual touch to nine equally spaced points, 2 cm apart, along a line from the subject’s cheek to her neck. This panel shows the location of stimulation points along the study subject’s face and neck. Photo credit: Tyson Aflalo, California Institute of Technology. The face is masked to obscure identity per publisher’s request. (B) Percentage of the neuronal population significantly modulated by touch to each stimulation location (p<0.05, false discovery rate corrected, shown as mean ± 95% CI, n = 585 units). (C) Representative neuronal responses showing the firing rate at each stimulation site as a function of time (mean ± 95% CI; n = 10 trials). (D) Representative examples of neuronal responses and Gaussian fits used to estimate receptive field size (for full description, see 'Materials and methods: Receptive field size estimation'). Briefly, for each neuron demonstrating a differential response to touch to each of the nine fields, we identified the preferred site of stimulus delivery as the site associated with the largest firing rate. Next, we fit a Gaussian model to the average responses at the nine sites, with the mean/center of the model fixed at the preferred response site. The receptive field size was estimated as the full width at half maximum. In each of the examples depicted, the colored lines represent the Gaussian model fit to the average responses. The number of units included in the analysis for each example site is indicated in the title of each subplot (as both the absolute number of neurons and as a percentage of the recorded neuronal population). The receptive field size was described as the full width at half maximum, shown in the title of each subplot. In each subplot, the x-axis indicates the stimulation site. The y-axis is a standard (z) score. Hz: Hertz; cm: centimeter.