Thursday 13 January 2011

The penis and sexual pleasure

Now this is an interesting study: "Self-ratings of genital anatomy, sexual sensitivity and function in men using the 'Self-Assessment of Genital Anatomy and Sexual Function, Male' questionnaire" (PDF).

It's a study of self-assessed ratings of sexual pleasure, orgasm intensity, and similar items by area. The study included 81 healthy men. One weakness of the study was that only eleven men were uncircumcised; this shouldn't bias the results, but it does mean that the foreskin's scores are known with less precision than those for other areas.

The key results were as follows:

Overall discrimination between genital areas was highly significant (mixed-model anova, P = 0.001) for ratings of 'sexual pleasure', 'orgasm intensity' and 'orgasm effort', but was not significant for 'discomfort/pain'. Ranked by degree of 'sexual pleasure', the area 'underside of the glans' was highest, followed by 'underside of the penile shaft', 'upper side of the glans', 'left and right sides of the glans', 'one or both sides of the penis', 'upper side of the penile shaft', 'foreskin' (11 subjects), 'skin between the scrotum and anus', 'back side of the scrotum', 'front side of the scrotum', and 'around anus', but not all pair differences were significant. The rank order was similar for 'orgasm intensity', but less similar and with fewer significant pair differences for 'orgasm effort'.

What this means, effectively, is that the foreskin is the least sensitive of all areas of the penis, when "sensitive" is defined as "capable of producing sexual pleasure or orgasm".

This is no great surprise to me. It's entirely consistent with the bulk of evidence indicating that the foreskin can be removed without adverse effects on sexual satisfaction, which would seem inconsistent with the foreskin playing a major role in sexual pleasure. But it may come as a surprise to those who were mislead by studies such as Sorrells et al., which (erroneously) presented the foreskin as the most sensitive part of the penis. Why?

Well, as Prof. Morris and I noted (among other points) in our critique of Sorrells' paper:

The authors conclude that ‘circumcision ablates the most sensitive parts of the penis’, although they only tested the ability of subjects to detect the lightest touch. Meissner’s corpuscles, being light-touch receptors, would be expected to cause such a measurement to exaggerate the sensitivity of the prepuce. However, sensitivity, particularly when discussing erogenous sensation, depends on several different modes of stimulation and their interaction. In addition, sexual sensation depends upon the types of mechanical stimulation generated during intercourse, which might in turn be influenced by circumcision status. Thus circumcision has the potential to either increase or decrease sexual sensation.

Put bluntly, the two studies measured completely different things. Sorrells et al tested response to having a nylon filament pressed against the skin; Schober assessed response to sexual stimulation. And the two are not the same at all.

2 comments:

sandz said...

Sorry, Jake, but you can't use the Schober study to demonstrate that the foreskin is less sensitive than the glans (or any other penile part)! The study did not reach STATISTICAL SIGNIFICANCE in terms of foreskin investigation. For this reason, Schober didn't even bother to enter the foreskin ratings or values at all in Table 1of the study! And she doesn't mention the foreskin at all in the study discussion.
But there's a further reason for me to criticise your use/abuse of Schober's study:
It is probably fair to say that there is a “circumcision culture” in the USA (well over 70% of US men are circumcised), and many American women don’t like the look of what they’re not used to, and consider the foreskin to be unclean, if not ugly.
The study's ratings were significantly affected by the men's sexual partners and presumably their preferences. So, if a partner avoided the foreskin or paid it scant attention (for example out of personal prejudice), this would very likely have affected the erotic value ("rating") that the intact men placed on their foreskin.
The Schober study isn't relevant here!

Jake said...

"The study did not reach STATISTICAL SIGNIFICANCE in terms of foreskin investigation" -- wrong, I'm afraid. The authors did not test for statistical significance, due to the small number of samples. That's a weakness of the study, as I mentioned in my post above, but it isn't the same thing as failing to achieve significance.

"So, if a partner avoided the foreskin or paid it scant attention (for example out of personal prejudice), this would very likely have affected the erotic value ("rating") that the intact men placed on their foreskin." -- that's not a logical argument, because it's difficult to avoid contact with the foreskin during most sexual activity (one can hardly leave it in the corridor outside!).