Five experiments explored short-term memory and incidental learning for random visual spatio-temporal sequences. In each experiment, human observers saw samples of 8 Hz temporally-modulated 1D or 2D contrast noise sequences whose members were either uncorrelated across an entire one-second long stimulus sequence, or comprised two frozen noise sequences that repeated identically between a stimulus’ first and second 500 ms halves (“Repeated” noise). Presented with randomly intermixed stimuli of both types, observers judged whether each sequence repeated or not. Additionally, a particular exemplar of Repeated noise (a frozen or “Fixed Repeated” noise) was interspersed multiple times within a block of trials. As previously shown with auditory frozen noise stimuli (Agus et al., 2010) recognition performance (d’) increased with successive presentations of a Fixed Repeated stimulus, and exceeded performance with regular Repeated noise. However, unlike the case with auditory stimuli, learning of random visual stimuli was slow and gradual, rather than fast and abrupt. Reverse correlation revealed that contrasts occupying particular temporal positions within a sequence had disproportionately heavy weight in observers’ judgments. A subsequent experiment suggested that this result arose from observers’ uncertainty about the temporal mid-point of the noise sequences. Additionally, discrimination performance fell dramatically when a sequence of contrast values was repeated, but in reverse (“mirror image”) order. This poor performance with temporal mirror images is strikingly different from vision's exquisite sensitivity to spatial mirror images.

People know surprisingly little about their own visual behavior, which can be problematic when learning or executing complex visual tasks such as search of medical images. We investigated whether providing observers with online information about their eye position during search would help them recall their own fixations immediately afterwards. Seventeen observers searched for various objects in “Where's Waldo” images for 3 s. On two-thirds of trials, observers made target present/absent responses. On the other third (critical trials), they were asked to click twelve locations in the scene where they thought they had just fixated. On half of the trials, a gaze-contingent window showed observers their current eye position as a 7.5° diameter “spotlight.” The spotlight “illuminated” everything fixated, while the rest of the display was still visible but dimmer. Performance was quantified as the overlap of circles centered on the actual fixations and centered on the reported fixations. Replicating prior work, this overlap was quite low (26%), far from ceiling (66%) and quite close to chance performance (21%). Performance was only slightly better in the spotlight condition (28%, p = 0.03). Giving observers information about their fixation locations by dimming the periphery improved memory for those fixations modestly, at best.

As a promising imaging modality, digital breast tomosynthesis (DBT) leads to better diagnostic performance than traditional full-field digital mammograms (FFDM) alone. DBT allows different planes of the breast to be visualized, reducing occlusion from overlapping tissue. Although DBT is gaining popularity, best practices for search strategies in this medium are unclear. Eye tracking allowed us to describe search patterns adopted by radiologists searching DBT and FFDM images. Eleven radiologists examined eight DBT and FFDM cases. Observers marked suspicious masses with mouse clicks. Eye position was recorded at 1000 Hz and was coregistered with slice/depth plane as the radiologist scrolled through the DBT images, allowing a 3-D representation of eye position. Hit rate for masses was higher for tomography cases than 2-D cases and DBT led to lower false positive rates. However, search duration was much longer for DBT cases than FFDM. DBT was associated with longer fixations but similar saccadic amplitude compared with FFDM. When comparing radiologists' eye movements to a previous study, which tracked eye movements as radiologists read chest CT, we found DBT viewers did not align with previously identified "driller" or "scanner" strategies, although their search strategy most closely aligns with a type of vigorous drilling strategy.