The near-perfect correlation between mental imagery scanning times (averaged across subjects) and interobject distances on imaged maps has been cited as evidence for Kosslyn's (1981) analog theory of mental imagery. Present results (1) indicate that individual subjects' scanning-time/distance correlations vary as a function of instructional set (and, hence, a priori expectations), and (2)reveal a large degree of individual variability in scanning-time/distance correlations. Kosslyn, Ball, and Reiser (1978) found that scanning times between objects on a mental image of a map (averaged across subjects) correlated +.97 with interobject distances on the original map. From this high correlation, Kosslyn et al. inferred that the distances between different objects in the viewing field were relatively preserved in the images (analog representations) of that field (Kosslyn, 1981; Kosslyn et al., 1978;Kosslyn, Pinker, Smith, and Shwartz, 1979). Unfortunately, the scanning-time/distance correlations for individual subjects were not reported. This absence of data was regrettable, given Kosslyn, Brunn, Cave, and Wallach's (1984) recent demonstration of large individual differences in imagery tasks other than scanning tasks. Because the analog model purports to describe a perception-like process occurring within individuals, the first goal of the present study was to investigate individual subjects' scanning-time/distance correlations.As suggested by Finke and Shepard (in press), the second goal of the present study was to investigate an alternative determinant of mental imagery scanning results. Pylyshyn (1981) argued that the imagery-scanning task was "cognitively penetrable" (p. 21) (i.e., a task in which performance varies in a rationally explicable manner with subjects' beliefs, expectations, knowledge, or goals). According to Kosslyn (1981), "cognitive penetration is important insofar as it demonstrates that properties of strucThis research was supported in part by funds from the National Institute of Mental Health, PHS, MH3649I, and the Wake Forest University Research and Publication Fund to Charles L. Richman. This experiment was reported at the annual meeting of the Midwestern Psychological Association, Chicago, IL, April, 1984.We thankMelanie Payne, Donald Routh, Harriet Shaklee, and the reviewers for their constructive criticisms of earlier drafts of this paper. We are also indebted to DeeNortonfor his invaluable statistical guidance. Requests for reprints should be sent to David B. Goldston, Department of Psychology, The University of Iowa, Iowa City, IA 52242. tures or processes are not fixed. We have claimed that the properties of the visual buffer are innately determined and they should not be subject to cognitive penetration" (p. 56). Because the analog theory cannot account for the possible effects of beliefs and expectations without the hypothesis of extra variables (and hence, extra degrees of freedom which negate the theory's predictive power), cognitive penetrability is a viable challenge to the notion...