All participants in Experiment 1a saw words presented in either a blurred or a clear font. Immediately following the presentation of each word, the participants verbally gave JOLs on a scale of 1–100. We used a multilist method so that any experience-based changes in JOLs, recall, or resolution would be evident (cf. Castel, 2008; deWinstanley & Bjork, 2004). If participants did perceive any mnemonic effects of disfluency, it is likely that their JOLs on subsequent lists would change accordingly and that resolution would improve across lists. Since blurred words should be perceived as less fluent than clear words, we anticipated that JOLs would be lower for the blurred words than for the clear words. The pattern of recall performance would help determine how visual distortion affects memory, providing further insight as to the extent and/or limitations of the perceptual-disfluency effect.
A group of 25 undergraduates enrolled in introductory-level psychology courses at the University of California, Los Angeles, participated for course credit. Each participant was tested individually.
A selection of 110 words were taken from the English Lexicon Project database and normed for frequency and length (Balota et al., 2007). The words had an average log HAL frequency of 9.6 (i.e., relatively common) and an average length of 5.29 letters. The words were randomly divided into four lists of 26 words each, with the six remaining words being used as examples at the beginning of the experiment. Each list contained equal numbers of clear and blurred words randomly distributed throughout the list. The first and last words of each list were eliminated from the analysis to account for primacy and recency effects, leaving 24 key words, 12 blurred and 12 clear, in each list. The lists were counterbalanced so that each list appeared equally often in the first, second, third, and fourth positions. Blurred words were distorted using a computer program to disperse the pixels in each letter by 10%, which pilot data had indicated was enough to noticeably blur the words, but not enough to impede people’s ability to read them. See the Appendix for an example of the stimuli.
The clarity of the words was manipulated within subjects. Participants saw four lists of 26 words, and each word was presented for 0.5 s in black, size 44 font on a white background. Equal numbers of words were presented in regular (i.e., clear) font and in blurred font. The clarity of the words was counterbalanced so that all words were presented equally often across participants in clear or in blurred font. After each word was presented, the participants were given 2 s to give a JOL by rating, on a scale of 1 (not at all confident) to 100 (completely confident), how confident they were that they would recall that item on a later test. Participants were instructed to say “0” if they had not been able to read the word. Prior to the first list, participants viewed six example words (three blurred and three clear) and were asked to practice making confidence judgments. Any remaining questions were answered before the participants began with the first list.
Immediately after each list, the participants engaged in a 10-s distractor task that involved counting backward by multiples of three. The starting number differed on each list. After the distractor task, participants were asked to recall out loud as many words as they could remember from the previous list. The participants did not receive feedback. This process was repeated three times, for a total of four lists.
The alpha level was set to .05 for all inferential statistics, and all effect sizes are reported in terms of η
for ANOVAs or of Cohen’s d for t tests. Across all 25 participants, in 28 cases a participant responded “0” in the judgment phase, to indicate that he or she had not seen the previous word. Twenty-two of those words were blurred and six were clear. These words were removed from all analyses, but we report the unconditionalized data as well. No single participant said “0” to more than five out of the 104 words that he or she saw, and no single word received a JOL of “0” more than twice.
Judgments of learning
JOLs were analyzed in a 2 (format: blurred, clear) × 4 (list: 1, 2, 3, 4) ANOVA. As can be seen in the top panel of Fig. 1, participants gave significantly higher JOLs to clear words (M = 58.76, SE = 3.79) than to blurred words (M = 48.34, SE = 3.71), F(1, 24) = 18.84, η
= .44. There was also a significant effect of list, F(3, 72) = 21.74, η
= .48, indicating that JOLs decreased across lists, regardless of format. We also found a borderline interaction between list and format, F(3, 72) = 2.77, p = .05, η
= .10. Paired-samples t tests indicated that within each list, clear words were given significantly higher JOLs than were blurred words, with an average d of 0.5. Within each format, participants gave the highest JOLs in List 1 (blurred, M = 59.94, SE = 5.05; clear, M = 74.22, SE = 4.62), but the JOLs decreased in subsequent lists, leveling off in Lists 3 and 4.
The recall data were analyzed in a 2 (format) × 4 (list) ANOVA and are reported as percentages. As is shown in the bottom panel of Fig. 1, there was no interaction or effect of list, but there was a marginal effect of format, F(1, 24) = 3.16, p = .09, η
= .12. More clear words (M = 29.05, SE = 2.46) were recalled than blurred words (M = 25.27, SE = 2.25).
We used the Goodman–Kruskal gamma correlation as a nonparametric measure of the association between format, JOLs, and recall (Nelson, 1984). This analysis was conducted to examine participants’ metacognitive accuracy—that is, whether they were actually more likely to recall a particular word if they gave it a higher JOL than if they gave it a lower JOL. For both blurred and clear words, resolution was significantly different from zero, G = .27, SE = .05, t(24) = 5.70, and G = .27, SE = .06, t(24) = 4.30, respectively. These data indicate that participants were generally more likely to remember words to which they had given higher JOLs. There was no main effect of format or of list on resolution, but there was an interaction between list and format, F(3, 45) = 3.20, η
= .176: Resolution increased for blurred words and decreased for clear words across lists.
The same analyses with all words included revealed an identical pattern: Clear words received significantly higher JOLs than did blurred words, F(1, 24) = 20.26, η
= .46, and JOLs decreased across lists regardless of format, F(3, 72) = 20.77, η
= .46. We also saw a marginal interaction with a small effect size between list and format, F(3, 72) = 2.31, p = .08, η
= .09. There was no interaction or effect of list on recall, but there was a marginal effect of format on recall, F(1, 24) = 3.76, p = .06, η
= .14. The gamma correlations were significantly different from zero, G = .30, SE = .05, t(24) = 6.28, and G = .29, SE = .04, t(24) = 4.72, for blurred and clear words, respectively. There was no main effect of format or of list on resolution, but the interaction between those two variables was marginal, F(3, 48) = 2.28, p = .09, η
= .13. The unconditionalized data showed the same pattern as in the main analysis, of the resolution for blurred words increasing across lists as the resolution for clear words decreased across lists. The similarities between the conditionalized and unconditionalized data indicated that item effects did not sway our conditionalized results.
In Experiment 1a, we examined JOLs and recall for blurred and clear words. As expected, we found that JOLs were higher for clear than for blurred words. Interestingly, resolution improved for blurred words and worsened for clear words across lists, indicating that participants were able to adjust their JOLs appropriately for the disfluent words. Participants may have been aware that they were not remembering the blurred words very often, and adjusted their JOLs on subsequent lists accordingly; why resolution did not also improve for clear words, however, is uncertain.
We did not find support for a desirable-difficulty explanation, but we also did not clearly support one of the other two theories. Since clear words were recalled only marginally more than blurred words, it was unclear whether this level of visual distortion was only a basic manipulation of visual acuity, as in Lindenberger et al. (2001), or whether deciphering the blurred words required a high enough cognitive demand to impair recall, as in Glass (2007). Another possibility is that the within-subjects design masked any unique benefit for disfluent items. For example, Alter et al. (2007) showed that merely having a title in a disfluent font caused participants to process the content below it more deeply. If seeing even one blurred word induced participants to deeply process all of the words on that list, we would not see a perceptual-interference effect within subjects. Experiment 1b addressed this issue, in that the disfluency manipulation was presented to only half of the participants.