The Midstream Order Deficit

When many impressions follow in excessively rapid succession in time, although we may be distinctly aware that they occupy some duration, and are not simultaneous, we may be quite at a loss to tell which comes first and which last- William James (1890), The Principles of Psychology, ch. 15.

The phenomenon James informally reported may be the same as what we have experimentally documented and term the Midstream Order Deficit ( Holcombe, Kanwisher, & Treisman, 2001; PDF; related abstract) is a difficulty in apprehending the order of successive items in the middle of a rapidly presented stream.

Subjects are asked to report the order of the four letters, beginning with any letter. In a number of experiments, accuracy was much lower when the letters were presented several times (the Cycling condition) than when they were presented once (the Single condition).


Single condition

NOTE: these movies are not an exact duplication of the conditions of the actual experiments, which is important because the midstream order deficit is sensitive to the rate of presentation and the smoothness of the presentation. Movie performance depends on your particular computer, web browser, web browser version, and plugin version.

Cycling condition

Subjects know that in the cycling condition the same sequence is presented over and over and that they can begin their report with any letter. Thus in the above cycling condition DMPG, MPGD, PGDM, and GDMP were all counted as correct, yet still subjects did much worse in the cycling condition.

What it means

The Midstream Order Deficit does NOT occur due to an attentional blink

The data from our experiments suggests that in the conditions of our experiments, no attentional blink occurred. See the paper for more info.


A similar effect occurs for repeated sequences of auditory stimuli (Warren, Obusek, Farmer, & Warren, 1969), and for repeated sequences with one visual, one auditory, and one tactile stimulus (Hirsh, 1976). This suggests that a central attentional limit prevents ordering of rapid sequences.

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