Measuring what's in your mind's eye: Afterimagery as a reference point for measuring individual differences in visual imagery.

We present a novel yet simple approach to measuring individual differences in visual imagery, in which people compare the quality of voluntarily generated visual images to the quality of (eyes-closed) negative afterimages. In laboratory testing (n = 98), many participants rated their own imagery of a face or a letter A to be similar or even stronger - on each of several experiential dimensions - than an afterimage of a face or letter. Dimensions were brightness, sharpness, detail, and two dimensions which deconstruct and challenge a simple distinction between associator-versus projector-imagers. Other participants rated their voluntary images to be weaker than afterimages, indicating qualitative differences between participants. This replicated data from a large-sample pilot, conducted under less formal conditions. Participants mostly expressed that their comparative ratings were accurate. Over the pilot and main study, ratings correlated with 3 standard self-report instruments for visual imagery, supporting the construct validity of our measure. Participants visually rendered the brightness and sharpness of their afterimages on a computer screen, allowing (a) depiction of the baseline against which voluntary images were being compared and (b) calculation that variation in afterimagery strength was independent of the strength of voluntary images, and cannot account for variance in our comparative ratings of voluntary imagery. As a method of quantifying the range of visual imagery experience from aphantasics to hyperphantasics, in healthy and clinical populations, our approach may be less metacognitively contaminated and more accurate than widely-used yet criticised self-report instruments of imagery, e.g. those comparing imagery vividness to real seeing.