Question

1. Kosslyn’s (1973) research showed that imagery and perception share some of the same mechanisms.
   1. Describe the Kosslyn’s experimental procedure.
   2. What were the results of these experiments?
   3. What specific conclusion did Kosslyn reach about imagery and perception?

Answer 1

Procedure The participants were tested individually, sitting 75 cm from a computer screen. Each participant performed the MI, FV, and II tasks. A given participant performed the three conditions with a single pattern of dots on all trials in a given task. However, the pattern of dots was different in each of the tasks. We counterbalanced over participants which configuration of dots was used for each task. In each task, participants first performed a practice block of 48 trials. The computer provided feedback, and trials on which there were errors were repeated at the end of the block. Then, in each task, six blocks of 48 experimental trials were presented with no feedback, and trials on which there were errors were repeated at the end of each block. The order of the trials was randomized, except that no more than three yes or three no trials could occur in a row. The onset of the arrow started a timer, which was stopped when one of the two response keys was pressed. RTs and the nature of the response were recorded. Because we were interested in the correlations among slopes, we needed to test the participants in the same experimental situation. However, to compare the mean slopes of the best-fitting lines, we had to counterbalance the order of the tasks. In a pilot study, we observed that the participants’ scanning efficiency in the II task correlated most strongly with their scanning efficiency in the MI task; thus, to avoid possible transfer of general processes between these tasks (which potentially could have accounted for the correlations), we chose to administer the FV task between the two tasks that were exhibiting the strongest correlation in the pilot study. Thus, we assigned participants to one of two counterbalancing groups. In Group 1 (18 participants), the order was MI, FV, and II; in Group 2 (18 participants), this order was reversed. Participants were asked to follow the written instructions displayed on the screen. A 5-min break was provided between each task. At the end of the experiment, participants completed a debriefing questionnaire to ensure that they had no idea of the purpose of the experiment and that they followed the instructions at least 75% of the time in each of the tasks. MItask.We began by showing the participantsthe pattern of dots on a hard-copy printout, and we asked them to draw the locations of the dots from memory on a blank sheet of paper, with the empty 19 19 cm black frame printed on it.We printed a hard copy of each of the original patterns on transparency sheets. In order to compare their drawings with the original pattern, participants superimposed the transparency on their drawings. Participants were asked to correct their drawings without the transparency and to then superimpose the transparency a second time. The draw-and-study procedure was repeated until all dots were drawn within 0.35 cm of their actual location. Depending on the participant, 1–7 drawings were required to reach this criterion. The draw-and-study procedure was an attempt to ensure that all participants started the task having the same knowledge of the positions of the dots; thus, the participants’ ability to memorize the dots during the course of the task would not affect individual differences in RTs or ERs. The participants were told that they would be cued to visualize this pattern. On each trial of the task itself (as illustrated in Figure 2), a fixation point first appeared in the middle of the screen for 1 sec. The pattern of four dots then appeared for 2 sec, which cued the participants to form the image after the mask (multiple black crossing lines on a white background; see Figure 2); the mask was displayed for 100 msec in order to disrupt any residual iconic image. Following this, an arrow appeared on the screen in the black frame and remained visible until the participants responded (see Figure 2). The participants were instructed to decide as quickly and accurately as possible whether the arrow pointed to a location previously occupied by one of the dots. If so, they were to press one key with their dominant hand (labeled with a “Y” on a green sticker); if not, they were to press the other key with their other hand (labeled with a “N” on a red sticker). At the beginning of the task, an example of a yes trial was presented by simultaneously displaying the pattern of dots and an arrow that pointed at one of them. FV task. The task and procedure were the same as those in the MI task, except that the participants did not memorize the pattern in advance. The trial structure was as follows: On each trial, a fixation point was presented in the center of the screen for 1 sec; the pattern of four dots then appeared for 1 sec in the 19 19 cm black frame; an arrow appeared along with the dots in the frame and remained visible until one of the response keys was pressed (see Figure 2). II task. The task and procedure were the same as those in the FV task, except that the pattern of dots appeared along with an arrow in the 19 19 cm frame, and this display was visible for 250 msec before it disappeared (but the outside square frame remained visible; see Figure 2). We presented the dots and the arrow simultaneously because we were concerned that, given the short duration of the presentation of the stimuli, displaying the arrow after the dots could have masked them. If so, this would have introduced spatial imprecision, which would in turn have contaminated our estimates of the scanning times.

Results As a first step, we analyzed RTs and ERs to determine whether we replicated earlier findings of studies that used this scanning paradigm. Following this, we compared the steepness of the slopes of the best-fitting lines, the height of the intercepts, and the ERs in the three tasks. We then analyzed the relationship between individual differences in performance of the three tasks. Preliminary analyses did not reveal any effect of—or interaction with—gender or the specific patterns. The order of the tasks also did not affect the results, except for the height of the intercept in the II task. This was higher in Group 2, which performed the II task first [M 509 msec for Group 2, as compared with M 445 msec for Group 1; t(34) 3.64, p .005]. We found no effect of the order of the tasks on the other measures. Although we did not use the full range of possible counterbalancing orders, the fact that we found virtually no differences between the most extreme orders—formed by switching the first and last tasks—is strong evidence that neither practice nor fatigue greatly affected the results. Thus, we pooled the data for the two counterbalancing groups, as well for males and females and for the different patterns, and we will not address these factors in the following description of the results

Analysis of RTs and ERs We analyzed separately the RTs from correct responses on yes and no trials, because we expected participants to scan the entire distances in the yes trials, but not always to do so in the no trials; that is, when it became obvious that the trajectory was going to miss a dot, participants may simply have stopped scanning, and we had no way to estimate at what point such a judgment may have been made. Prior to the analyses, we eliminated outliers, which were defined as RTs greater than 2 SDs from the mean of that distance for that participant. In the yes trials, we also considered RTs under 250 msec as outliers, because such times could not have reflected the cognitive processes of interest (i.e., the scanning processes). Outliers occurred on 4.2% of the trialsin the MI task, and on 3.1% in the two visual scanning tasks. Finally, trials on which participants made errors were repeated on average 1.11 times. Yes trials. In order to discover whether we replicated previous findings, we first averaged the RTs over the trials for each distance in each task for each participant; then, we conducted separate ANOVAs on data from the three tasks. In the MI task, we found that different distances between the tip of an arrow and the previous location of a target dot required different amounts of time to scan [F(5,175) 13.47, p .0005]. As is evident in Figure 3, the best-fitting linear function calculated by the method of leastsquaresrevealed that RTsincreased linearly with distance [F(1,35) 62.89, p .0005]. The Bravais–Pearson correlation between times and distance was r(4) .93, p .01. These results replicated those reported by Finke and Pinker (1982, 1983) and suggest that participants did use image scanning to perform this task. We conducted the same analysis on the data from the FV task and found that RTs varied for the different distances [F(5,175) 56.55, p .0005]. Moreover, RTs increased linearly with increasing distance [F(1,35) 125.07, p .0005]; as is shown in Figure 3, RTs were correlated with distance [r(4) .99, p .01]. These results are consistent with those reported by previous studies, even though we used a different scanning paradigm, which confirmed the robustness of the scanning effect (Beech, 1980; Denis & Cocude, 1989; Pinker, 1980). Finally, in the II task, we processed the data as follows: We included the 250 msec of presentation of the stimulus in the RTs to take into account the possibility that some participants could have started to scan before the offset of the stimulus. In addition, we did not include RTs from trials in which participants responded in less than 250 msec,which allowed us to remove trials in which scanning could have been completed while the stimulus was present. RTs again varied with distance [F(5,175) 79.1, p .0005], and RTs increased linearly with increasing distance [F(1,35) 173.88, p .0005]. As is illustrated in Figure 3, we again found a strong positive correlation between scanning times and distance [r(4) .98, p .01]. These results are of great interest not only because they provide evidence that even with limited eye movements (at most, one saccade), participants were able to scan the distances between the tip of an arrow and a target dot, but also because they provide a first hint that mental image representations may be similar to iconic image representations. It should be noted that the participants reported during the postexperiment debriefing that they did not use mental images in the two perceptual tasks (FV and II). No trials. We excluded from our analysis 8 of the 24 arrows because they missed the dots by more than 90º, and we could not associate the arrows with a specific distance.The 16 remaining arrows were assigned to one of two groups of 8 arrows: Half were less than 4 cm from the nearest yes dot and half were more than 5 cm from the nearest yes dot. There was no effect of distance on the no RTs in any of the three tasks [F(1,35) 1, n.s., in the MI task; F(1,35) 1, n.s., in the FV task; and F(1,35) 1, n.s., in the II task]. The lack of effect of distance on the RTs in the no trials is probably a result of the fact that we designed the arrows to miss all the dots by more than 40º; thus, the discrimination was very easy. Participants were faster on the no trials than on the yes trials, both in the II task (with means of 306 vs. 551 msec, respectively) [t(35) 19.92, p .0001] and in the MI task (862 vs. 942 msec, respectively) [t(35) 4.25, p .0005]. However, in the FV task, participants were not significantly faster on the no trials than they were on the yes trials (with means of 607 vs. 624 msec) [t(35) 1.09, n.s.]. Thus, in the MI task and the II task, given the angles chosen, participants did not necessarily need to scan to decide whether the arrow missed the dots; we suggest that a fast attentional process (distinct from imagery) could be sufficient to make the necessary discrimination. Given that RTs did not increase with distance in the no trialsfor the FV trials, we cannot inferthat participantsscanned during these trials; instead, the participants may simply have “doublechecked” the no trials when the pattern was in free view in order to ensure that the arrow did, in fact, miss the dots. If so, they would not be fasterfor no trials, but they also would not require more time with longer distances. However, if a smaller angle had been chosen, we would have probably observed an increase of the RTs with increasing distance (as reported by Finke & Pinker, 1982, 1983).