The gist of the abnormal: Above-chance medical decision making in the blink of an eye

Abstract

Very fast extraction of global structural and statistical regularities allows us to access the “gist” – the basic meaning - of real world images in as little as 20 miliseconds. Gist processing is central to effcient assesment and orienting in complex environments. It is probable that this ability is based on our extensive experience with the regularities of the natural world. If that is so, would experts develop an ability to extract the gist from artifical stimuli (e.g. medical images) with which they have extensive visual experience? Anecdotally, experts report some ability to categorize images as normal or abnormal before actually finding an abnormality. We tested the reality of this perception in two expert populations; radiologists and cytologists. Observers viewed brief (250–2000 milliseconds) presentations of medical images. The presence of abnormality was randomized across trials. The task was to rate the abnormality of an image on a 0–100 analog scale and then to attempt to localize that abnormality on a subsequent screen showing only the outline of the image. Both groups of experts had above chance performance for detecting subtle abnormalities at all stimulus durations (cytologists D’ ~1.2 and radiologists D’ ~1) while non-expert control groups did not differ from chance (D’~0.23, D’~0.25). Further, the expert’s ability to localize these abnormalities was at chance levels suggesting that categorization was based on a global signal and not on fortuitous attention to a localized target. It is possible that this global signal could be exploited to improve clinical performance.

Attention and the Cognitive Penetrability of Perception

“…For example, radiologists reliably identify abnormalities in rapidly presented (200ms) chest radiographs. Eyetracking studies corroborate these results by revealing substantially different scan patterns between experts and controls: expert radiologists make fewer total saccadic eye-movements and fixate more quickly on abnormalities [Drew et al 2013;Evans et al 2013]. These and many other cases of empirically studied perceptual expertise are candidate examples of epistemically enhancing cognitive penetration.…”

Worth a quick look? Initial scene previews can guide eye movements as a function of domain-specific expertise but can also have unforeseen costs.

“…The ability to exploit the initial glimpse of the scene is at the core of the holistic model (Kundel et al, 2007) but is also a key component of scene perception research (Castelhano & Henderson, 2007;Torralba et al, 2006;Wolfe et al, 2011). By using the FPMW paradigm to control the contribution of the initial glimpse on subsequent search as a function of expertise, the present study extends previous eye-tracking research that has until now only been able to indirectly investigate these issues, either via tachistoscopic studies (Carmody et al, 1981;Kundel et al, 1975;Evans et al, 2013) or free viewing studies (Donovan & Litchfield, 2013;Kundel et al, 1978;Kundel et al, 2008;Manning et al, 2004).…”

A half-second glimpse often lets radiologists identify breast cancer cases even when viewing the mammogram of the opposite breast

“…No one would suggest that diagnosis should be based on these first glimpses. However, there is now a body of research, including the work reported here, that indicates that this sense of the gist of a medical image can be based on a measurable signal (5,12,15). Our goal, in the present paper, has been to investigate the nature of the signal that allows expert observers to classify mammograms as normal or abnormal at above chance levels after a brief exposure.…”

“…Experts often anecdotally report gistlike experiences with complex images in their domain of expertise. For instance, we have shown that radiologists can distinguish normal from abnormal mammograms at above-chance levels in as little as a quarter of a second, whereas nonexperts cannot (5). The gist of abnormality appears to be a global signal.…”

“…Moreover, the discriminations made on the basis of a first glimpse, while not random, are typically far from perfect. Returning to mammography, Evans et al (5) found that, although experts could classify mammograms Significance Discovering characteristics of a signal that indicates to medical experts the presence of cancer in a noninvasive screening technique in a blink of an eye has implications for improving cancer detection. Here we report two surprising facts about this signal.…”