13.21 Researchers studying pleasant touch sensations measured the firing frequency (impulses per second) of nerves that were stimulated by a light brushing stroke on the forearm and also recorded the subject’s numerical rating of how pleasant the sensation was. The accompanying data was read from a graph in the paper “Coding of Pleasant Touch by Unmyelinated Afferents in Humans”

(Nature Neuroscience, April 12, 2009).

Firing Frequency Pleasantness Rating 23 0.2 24 1.0 22 1.2 25 1.2 27 1.0 28 2.0 34 2.3 33 2.2 36 2.4 34 2.8

a. Estimate the mean change in pleasantness rating associated with an increase of 1 impulse per second in firing frequency using a 95% confidence interval.
Interpret the resulting interval.

b. Carry out a hypothesis test to decide if there is convincing evidence of a useful linear relationship between firing frequency and pleasantness rating.