Screen position effects on task performance in a delayed match to sample task.

Studies of working memory have used immediate and delayed recall of lists of items. Serial position effects are the phenomena where items at the beginning and end of a studied list are recalled differentially from items in the middle of the list. In matching versions of the task, study items may be presented serially or simultaneously in a grid. After a delay a single probe item is presented for which the participant determines whether or not it was in the study set. The effects of the position of an item when studied on a screen are currently not well understood and are the focus of the current work. Findings from a delayed match to sample task in 49 healthy young adults with 1 to 9 items presented in a 3 by 3 grid, demonstrate that the column of the studied items affect response time and accuracy. The effects of position on accuracy also significantly interact with task demands. The importance of screen position effects is demonstrated with simulations using the mean accuracies split by task demands and screen locations. Simulations demonstrate the possible range of accuracies based on screen effects when the number of trials presented to an individual is less than 20 for each task demand. This has important implications when a small number of trials are administered using randomly generated stimuli which is often the case in neuroimaging studies where tasks are delivered under constrained time limits.