Final answer:
Locus of control is not a dimension of mental abilities; it pertains to the degree of control individuals believe they have over events in their lives, unlike spatial aptitude, number aptitude, and perceptual speed which are cognitive abilities.
Step-by-step explanation:
The dimension that is not a dimension of mental abilities among the options provided is b) Locus of control. This term refers to the extent to which individuals believe they can control events affecting them. The other options, such as spatial aptitude, number aptitude, and perceptual speed, are considered cognitive abilities. Spatial aptitude refers to the capability to think in three dimensions, number aptitude involves the ability to work quickly and accurately with numbers, and perceptual speed is the ability to identify visual details quickly.