Point taken ... I checked, there is no revised edition listed for this book, and one must conclude the allusion in the Spencer book is not to the more recent work by Daryl Bem. SIDE NOTE: I made a point to check another paranormal compendium with an identical title by Rosemary Guiley, in case the OP was referring to that book rather than the Spencers'. Guiley's book contains no mention of erotic / sexual / pornographic anything. Having said that ... The perceived utility of using erotic (and / or other emotion-inducing) images in psychological experimentation on emotion, attention, and arousal dates back a long way. For example, Bem's much-publicized experiment(s) relied on images drawn from the International Affective Picture System (aka IAPS), which was in widespread use over 35 years ago.