Fig 1.
Speed ratings across textures.
(A) Magnitude estimates of speed obtained from an example subject. Normalized speed ratings for different textures are shown in different colors. Dots denote single trials (n = 6 per condition), and lines denote means. (B) Average speed rating for all subjects (n = 10). Dots denote the mean, and shaded areas denote the SEM. (C) Coefficients (slope versus intercept) of the linear regression relating speed ratings to speed. Error bars denote the SEM (n = 10). Data underlying this figure can be found in S1 Data.
Fig 2.
Speed discrimination within texture.
(A) Discrimination performance—as gauged by the proportion of trials judged faster than the reference (at 80 mm/s) versus speed—of an example subject for “thin corduroy” (black) and “metallic silk” (pink). (B) Performance averaged across subjects for all tested textures (n = 8 subjects for each texture). Error bars denote the SEM. (C) Weber fraction obtained from individual subjects (small dots) along with the respective means ± SEM (large dots and bars). Data underlying this figure can be found in S1 Data.
Fig 3.
Speed discrimination across textures.
(A, B) Discrimination performance—as gauged by the proportion of trials on which the comparison was judged to be faster than the reference versus speed—averaged across subjects for each texture pair. In (A), the reference and comparison were the same texture (reproduced from Fig 2, but organized by pairs). In (B), the reference and comparison were different textures. The color (black or red) depicts the texture used as reference. (C) PSE for the same (left, light) and different (right, dark) texture pairs. Error bars denote the SEM (n = 8 for each same pair, n = 9 subjects for each different pair). Stars reflect the outcome of a one-sample t test versus 80 mm/s (− denotes not significant, *p < 0.05, **p < 0.01, ***p < 0.001). The effect of texture on PSE was consistent with the results from the magnitude estimation experiment (Fig 1C, intercepts). Data underlying this figure can be found in S1 Data. PSE, point of subjective equality.
Fig 4.
Speed dependence of the responses of tactile nerve fibers.
(A) Spiking responses of two nerve fibers from each class (SA1, RA, and PC fibers) to two repeated presentations of 11 different textures scanned at three different speeds. (B) Mean firing rate across fibers of each type. Each color is a different texture (see legend at the bottom left); light gray represents the textures not used in the psychophysical experiments. Data underlying this figure can be found in S1 Data. PC, Pacinian corpuscle–associated; RA, rapidly adapting; SA1, slowly adapting type 1.
Fig 5.
(A) Rating of perceived speed (averaged across subjects) as a function of afferent FR (averaged across nerve fibers of each type) at the three tested speeds. Each color denotes a different texture (see legend in Fig 4). (B) Weber fractions as a function of afferent speed sensitivity (as indexed by the slope of the function relating afferent FR to speed). (C) Difference in PSE as a function of difference in FR at 80 mm/s (normalized using [a − b] / [a + b]). For all three psychophysical paradigms—speed rating, within-texture discrimination, and across-texture discrimination—PC FRs best account for the texture dependence of speed perception. Error bars denote the SEM. Data underlying this figure can be found in S1 Data. FR, firing rate; PC, Pacinian corpuscle–associated; PSE, point of subjective equality; RA, rapidly adapting; SA1, slowly adapting type 1; spk, spike.
Fig 6.
Speed dependence of the responses of cortical neurons.
(A) Spiking responses of four neurons in somatosensory cortex to five repeated presentations of 10 different textures scanned over the center of their RFs at two different speeds. Neurons #2 and #46 increase their rate with speed; neurons #18 and #9 do not. (B) Mean firing rate versus speed. Each color denotes a different texture (see legend at the bottom left). Data underlying this figure can be found in S1 Data. spk, spike.
Fig 7.
Speed coding in single cortical units.
(A) p-Value versus normalized regression slopes for each neuron. Black denotes cortical neurons, and red denotes nerve fibers. Marker type denotes cortical field or fiber type (see legend). The gray line denotes the threshold for significance (10−4). (B) Regression slope for each neuron, classified by area and fiber type (bars show the mean across neurons). (C) PC weight as a function of regression slope for each neuron. Neurons with higher PC input tend to be more sensitive to speed. Data underlying this figure can be found in S1 Data. PC, Pacinian corpuscle–associated; RA, rapidly adapting; SA1, slowly adapting type 1.
Fig 8.
Population coding of speed in somatosensory cortex.
(A) Speed decoding performance as a function of number of neurons within texture, including both speed-sensitive and speed-insensitive neurons. Each color denotes a different texture (see legend in Fig 6). (B) Speed decoding performance within (left) and across (right) textures, using A (n = 49), S (n = 25), and N (n = 24). Each colored dot is a different texture; the square and line denote the mean ± SD. (C) Speed ratings versus the mean firing rate of the entire cortical population. Each color denotes a different texture. (D) Speed rating versus the best-fitting linear combination of the mean firing rates of the two subpopulations of neurons (speed sensitive and insensitive). Data underlying this figure can be found in S1 Data. A, the entire population of neurons; N, the speed-insensitive subpopulation; S, the speed-sensitive subpopulation; spk, spike.