Other factors may have improved subjects' apparent memory capacity in our study. Unlike many prior studies, we used distinct objects that never repeated, which may have reduced interference between objects (Endress & Potter,
2014). Furthermore, many subjects reported using verbal strategies (e.g., “the pants are above the shoes”) to help remember displays. We suspect that such strategies would have been only minimally helpful, both because they seem to play a minimal role in long-term memory using comparable encoding times (e.g., Brady, Konkle, Gill, Oliva, & Alvarez,
2013)
4 and because they seem insufficient to attain the precision exhibited by visual spatial memory. Because verbally encoded spatial relations (such as “above” or “left”) offer only imprecise location information, we suspect that the main benefit of such verbal encoding was to reduce misassociations between objects (Lew, Pashler, & Vul,
in press) rather than encoding the locations themselves. Additionally, patterns of oculomotor movements and attentional shifts could have influenced performance by interfering with encoding in visual memory (Lawrence, Myerson, & Abrams,
2004). Although the uniform distribution of cluster centers in our study still mandates many changes of fixation, it is possible that clustering yields fewer eye movements and attentional shifts between objects in the same cluster, improving the fidelity of memories. Our presentation times were also longer than most visual working memory studies, which may have given subjects more time to encode objects. Given that performance appears to asymptote with display times shorter than those used in the current study (Bays, Gorgoraptis, Wee, Marshall, & Husain,
2011), our results may reflect how people encode stimuli when given enough time to thoroughly observe all objects. Varying the encoding time, delay time, or the environment statistics might reveal how people navigate the space of possible encoding schemes.