Department of Psychology
Midwestern Psychological Association’s Annual Meeting, Chicago
May 5, 2006
Jeremiah D. Still, Wah Pheow Tan & Veronica J. Dark
For more information e-mail: jeremiah@iastate.edu
Is the magnitude of the Attentional Blink affected by number of items or time?
Introduction
When two targets occur in a rapid serial visual presentation (RSVP) stream, the response to the second target (T2) is less accurate when it occurs 200-500 msec after the first target (T2). Raymond, Shapiro and Arnell (1992) described this as an Attentional Blink (AB).
Interference explanations of AB (e.g., Shapiro, Raymond, & Arnell, 1994) focus on interference caused by the intervening items, while the processing explanations of AB focus on processing time (e.g., Chun & Potter, 1995). Interference models predict that inserting more items in a time interval should increase the magnitude of the blink; processing models focus on time to process T1.
Most studies confound number of items and time between targets because items are presented at about 1 every 100 msec (e.g., 200 msec = lag 2 = 2 items; 500 msec = lag 5 = 5 items).
Experiment 1: Regular Distractor ISI
Experiment 2: Irregular Distractor ISI
Method
Number of items (1, 2, or 4 per lag) and Lag (2, 3, 4, 5, and 6) were varied within-subjects, so the number of items within a single lag varied as a function of the ISI.  Participants completed 225 experimental trials.
Method
 Number of items (more or less) and Lag (2, 3, 4, 5, and 6) were varied within-subjects, ISI duration varied randomly between items. Participants completed 150 experimental trials.
Results
Results
General Discussion
Interference explanations predict that presentation of more items per unit of time should produce a larger AB. Experiment 1 showed that increasing the number of items reduced the AB, but a salient temporal cue may have been responsible. Experiment 2 varied distractor ISIs in both a more and less condition.  AB magnitude remained unchanged.  It appears that time between T1 and T2 and not number of items is the important variable in AB magnitude. It was suggested that a salient temporal cue reduced the AB - for further investigation see Tan, Still and Dark (2006).
References
Chun, M. M. & Potter, M. C. (1995). A two-stage model for multiple  target detection in rapid  serial visual presentation. Journal of Experimental Psychology: Human Perception and Performance, 21(1), 109 – 127.
Raymond, J. E., Shapiro, K. L. & Arnell, K. M. (1992). Temporary suppression of visual processing in an RSVP task: an attentional blink? Journal of Experimental Psychology: Human Perception and Performance, 18(3), 849 – 860. Shapiro, K. L., Raymond, J. E., & Arnell, K. M. (1994). Temporal allocation of visual attention: Inhibition or interference? In D. Dagenbach & T. H. Carr (Eds.), Inhibitory mechanisms in attention, memory, and language (pp. 151 - 188). New York: Academic Press. Tan, W. P., Still, J. D., & Dark, V. J. (2006). Measuring the AB Effect in an Irregular RVSP Stream. Poster presented at the meeting of the Midwestern Psychological Association, Chicago, IL.
Experiment 1 Illustration
Experiment 2 Illustration
Discussion
Discussion
AB magnitude decreased as the number of items per unit of time increased, an effect opposite of that predicted by the interference models.
 A salient temporal cue in the 2 and 4 items/per lag conditions may have facilitated target processing. T1 and T2 may have been highlighted by their longer ISIs when embedded in the 2 and 4 items per lag conditions. Experiment 2 had irregular distractor ISIs in both a more and less items condition.
Unlike Experiment 1,  number of items per lag did not affect AB magnitude.
Overview
Participants identified two red letters in an RSVP stream of black letters. Letter duration was 24 msec each. Variations in the blank interstimulus interval (ISI) between letters eliminated the confound between time and number of items. Lag was defined as a 96-msec window of time.  The number of items within a single lag varied as a function of the ISI. The ISI before and after each target was 72 msec, preventing perceptual masking varying as a function of ISI.
17
13
9
5
1
0 msec
9
7
5
3
1
24 msec
5
4
3
2
1
72 msec
Lag 6
Lag 5
Lag 4
Lag 3
Lag 2
Distractor ISI
Table. Number of Items Between Targets