Specs for ChangeDetection2 (Programmer: Grant)

*10/03: Spoke to Grant and verified that Change Detection2 is actually Change Detection1, with all the minor changes that Hal wanted. In other words, Change Detection1 & 2 are NOT 2 completely different experiments.

Overview.

Subjects see displays of letters, which remains present for 1 second, disappears for 200 msec, and reappears until response. Subjects attempt to determine which letter was changed in the second frame. Forced-choice response (clicking mouse on the letter).

Design

12 blocks of trials, with 40 trials per block.

Subject condition: number of letters in first block (implicitly defining the rest as well)

One blocktype factor: NumberOfLetters

NumberOfLetters = 3, 5, 7, 9, 12, or 15 letters

Displays

Display consists of 15 positions (3 rows of letters X 5 columns). Grid should be evenly spaced. When display size < 15, select the positions to occupy at random.

Each trial involves two frames: Frame1 and Frame 2. Frame1 contains n letters in randomly chosen positions within the 15-position grid (n=displaysize). Frame2 is just like Frame1 except that one of the n letters has been switched for another letter.

Procedure

Present plus sign in center for 1 second; present frame1 for 1000 msec; take frame1 away for 200 msec; put up Frame2. Frame2 remains present until the subject clicks on the position of one of the letters in Frame2.

Program

Put up message to subject “In this block, look for any change (including change of case)”

Randomly select the letters in frame1 without replacement from the entire uppercase alphabet. Make frame2 by taking frame1 and randomly switching one of the letters in frame1 replacing it with a different letter.

Example of two displays you might see:

Frame1:

C F V

G E L

R W

Frame2:

C F V

G E L

B W

(Correct response would be to click on the B in Frame2 since that is the only letter identity that changed)

Instructions