Figure 1.
Timeline of an experimental trial.
At the start of each trial, participants were shown a grating, which they needed either to hold in memory (VSTM condition) or to project as a mental image on the computer screen at fixation (imagery condition). During the maintenance, a masked grating was presented on 50% of trials; participants were asked to indicate whether or not they had perceived it. They were then asked to perform an orientation discrimination judgment based on the memory/imagery item; this involved indicating whether a test stimulus was tilted to the left or right relative to the memory/imagery cue. At the end of each trial, participants were asked to provide a rating of the strength of their memory or imagery on a 1-9 scale. In addition, they were asked to match the contrast of the grating held by memory/imagery to the exemplars presented on the screen. In Experiments 2 and 3, VSTM/imagery involved colored shapes (rectangle) while the visual target was the same as in Experiment 1 (see figure 1B).
Figure 2.
The mean (n=14) sensitivity (d’) and bias in each condition.
In the “BL” condition, the memory cue was not shown and no VSTM or imagery was required. In the “task” condition, participants were engaged either in VSTM or in visual imagery. A) Engagement in VSTM increased visual detection sensitivity relative to baseline trials but not significantly; no such effect was found for imagery. B) Engagement in VSTM decreased the bias; a similar but nonsignificant trend was present in the imagery condition. C) The mean memory accuracy in congruent and incongruent trials. Detection performance is plotted by the function of VSTM/imagery cue-target orientation congruency. The Error bars indicate SDs from which between-subjects variance has been removed [15].
Figure 3.
Relationship between VSTM/imagery contrast/subjective strength and visual detection.
The Error bars indicate SDs from which between-subjects variance has been removed [15]. A) Mean (n=14) visual contrast of the memory/mental image on the contrast response scale as a function of performance in the detection task For VSTM, contrast was significantly higher for “hits” than for other trial types. For imagery, contrast was significantly higher for “hits” and “false alarms” than for “misses” and “correct rejections”.
B) Mean (n=14) subjective strength of the memory/mental image as a function of performance in the detection task. For VSTM, subjective strength was significantly higher for “hits” than for other trial types. For imagery, subjective strength was significantly higher for “misses” and “false alarms” than for “hits” and “correct rejections”.
Figure 4.
The mean (n=14) sensitivity (d’) and bias in Experiments 2 (panels A and B) and 3 (panels C and D).
The Error bars indicate ± 1 SEM.
Figure 5.
Mean subjective strength of VSTM in Experiment 2 (panel A) and imagery in Experiment 3 (Panel B) as a function of performance in the detection task.
The Error bars indicate Error bars indicate ± 1 SEM.