Individual psychometric functions for three experimental conditions, Experiment 1.

<p>The actual speed of the standard stimulus was always 81 mms⁻¹. Comparison speed is on the abscissa. The ordinate gives the proportion of responses in which the comparison stimulus was judged faster than the test stimulus. The three experimental conditions are: no adaptation (circles), adaptation in the same direction as the test speed (triangles), and adaptation in the opposite direction to the test speed (squares). The lines are the fitted logistic regression curves. Also shown are the PSEs given by the mean of the fitted logistic function. PSEs in the baseline condition were higher in all participants (perceived speed faster) than PSEs in the adaptation conditions.</p

Individual psychometric functions for three experimental conditions, Experiment 2.

<p>Format the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045438#pone-0045438-g004" target="_blank">Figure 4</a>. Data are plotted for three adaptation conditions: baseline (circles), in which both hands received adaptation in the same direction; same direction (triangles), in which the reference hand was adapted in the same direction as test, and the comparison hand was adapted in the opposite direction; and opposite direction (squares), in which the reference hand was adapted in the opposite direction to test, and the comparison hand was adapted in the same direction.</p

Perceived direction of the moving surface over time.

<p>The proportion of time each response was given is plotted over a four-minute period. Data are averaged over 10 s time bins. Error bars give the bootstrapped 95% confidence interval of the mean.</p

Design of Experiment 2.

<p>The three experimental conditions of Experiment 2.</p

Possible outcomes of Experiment 2.

<p>The first possibility is that matching the direction of the adapting and test stimuli leads to greater adaptation of perceived speed (first row). If this is the case, then the Opposite Direction condition should produce the highest PSE (smallest tSAE) and the Same Direction condition should produce the lowest PSE (greatest tSAE). This is because in the Same Direction condition, the direction of motion for the reference hand is matched at adaptation and test, whereas in the Opposite Direction condition, the motion for the reference hand at adaptation and test are in opposite directions. The second possibility is that the greatest adaptation occurs with an adapting stimulus moving in the opposite direction to the test (second row). In this case the Same Direction condition should produce the highest PSE (smallest tSAE) and the Opposite Direction condition should produce the lowest PSE (greatest tSAE). The third possibility is that the tSAE is insensitive to direction, with the adapting stimulus creating similar levels of adaptation regardless of its direction relative to test (third row). In this case, we would not expect to see any consistent differences across conditions.</p

The apparatus.

<p>A: Observers judged the relative speed of two different moving drums. (The subject of the photograph has given written informed consent to publication of their photograph.) B: One of the drums used to create tactile motion. Here, the stocking is pulled back to reveal the ridged rubber surface underneath.</p

Frequency histograms showing the timing of spikes relative to surface ridges (278 ms temporal period).

<p>The stimulus event time was recovered via ad-hoc observation of the spike data. Three key stages of run 2 are shown: 1) Top panel: the 30 s adaptation period; 2) middle panel: the first five top-ups; and 3) bottom panel: the last five top-ups. Shades give the rank order of the spikes after the onset of a given ridge.</p

Multiunit recording of neural activity in primary afferents exposed to prolonged tactile motion.

<p>A. Relative changes in the spiking activity during 30 s long adaptation phase. Data averaged over 5 s time bins. B. Level of spiking activity during twenty 5 s long top-up periods in the test phase, relative to the same baseline as in A.</p

Contact Force data.

<p>A: Contact force over time for the reference (black) and comparison (white) hands for one representative participant (DL) in the Same Direction condition. The session consisted of three successive runs, represented by one panel each. B: Mean contact force for the reference and comparison hands for each condition. Error bars on each pair of bars within the same condition are identical and represent 95% CI of their difference scores (comparison – reference).</p

Mean PSE (bars) across participants as a function of adaptation condition, Experiment 2.

<p>Error bars represent 95% confidence intervals of the mean. The symbols indicate the PSE obtained for each participant.</p