Figure 1.

Experimental design. Left, During the study phase, subjects were scanned while incidentally encoding a series of visually presented objects and greebles in a variant of the Posner cueing paradigm. Items were preceded by an arrow cue, pointing to a box on the left or right side of the screen. Subjects were to covertly shift attention to the cued box, in anticipation of an upcoming item. Items appeared after a variable duration (see Materials and Methods, Behavioral task) in either the cued location (validly cued trial) or the uncued location (invalidly cued trial). Subjects made a button press to indicate they had identified a real object or a greeble, regardless of whether the item appeared in the validly or invalidly cued location. Right, Following the study phase, subjects were administered a surprise memory test for the real objects. Subjects made one of four memory responses indicating whether they recognized the item from the previous study phase (old) or whether the object was unstudied (new), as well as their level of confidence in their decision (sure or unsure). If an old response was given, subjects were cued to make a source judgment for the location in which the item was studied (left or right).