My wife bought a vintagey shirt the other day. It’s long-sleeved, white, with colored letters on the front to the effect of “Tickle Me, Hug Me” etc., and a picture of Elmo below. I’ve searched the web in vain for a picture…and finally found one!
Then late last night, I discovered one of the tags from the purchase on her dresser, and I stopped immediately in my tracks. It looked like a plastic pillow inflated version of this:
I said to myself – that’s just like the logo of Love, American Style!
The vividness with which the logo and bits and pieces of the show (that damn title song) burst into my mind was impressive. I was 10 years old in 1973 (the show ended in January, 1974 – I had to look that up), trying to catch a bit of what my older sisters were watching. I knew it was risqué entertainment!
This experience reminded me of a recently published article by Mitchell (November, 2006, “Nonconscious Priming After 17 Years: Invulnerable Implicit Memory?“ in Psychological Science). Implicit memory is a form of memory not necessarily accompanied by a conscious experience of the memory act. Often we’ll realize that something had an effect on our behavior (Why am I humming White Christmas?) and we have no conscious (or explicit) recollection of how such a behavioral consequence might have occured (Muzak in the mall, maybe?). A short description is memory without awareness. This form of memory is spared after damage to the hippocampus, so anterograde amnesics typically have fully functional implicit memory.
We have implicit memory for differing types of material. Often a vague feeling of knowing will accompany our reasoning about an idea; this would be conceptual implicit memory. Other times implicit memory, as in the logo and song examples above, will be for some perceptual experience. Mitchell sums this up well and sets the stage for his experiment:
Theoretically, perceptual processes are engaged when there is an overlap of physical features between a target and a test cue (e.g., aardvark–aa_d_a_k in word-fragment completion). Thus, priming in perceptual tasks is facilitated by physical similarity, and can be diminished or even eliminated by physical changes between study and test. In contrast, conceptual processes are at work when semantic features overlap between study and test (e.g., animals as a test cue for aardvark in category-exemplar generation). Priming in perceptual tasks is theorized to be mediated by a perceptual representation system (Tulving & Schacter, 1990), and priming that is mediated by this system appears to be less affected by long retention intervals than is priming based on conceptual processes (Roediger & Geraci, 2005). Thus, picture-fragment identification—an unequivocally perceptual implicit task (Roediger & McDermott, 1993)—was employed in the present study.
In light of previous findings on the durability of priming, is it possible that priming is actually invulnerable to decay over time? More than 17 years ago—having found priming to be undiminished after an interval of 6 weeks—Brown and I wrote that “perhaps some residual effect of naming a picture persists indefinitely” (Mitchell & Brown, 1988, p. 220). The current investigation was conducted to push the envelope well beyond the longest interval previously tested (22 months), treating our audacious statement as a hypothesis.
So 17 years ago, participants were in Brown and Mitchell’s lab and saw and named some line drawings of objects (the so-called Snodgrass and Vanderwart drawings, which aren’t reproducible here). Later they had an explicit memory test for the items (in the same session and 6 weeks later).
Mitchell contacted the present participants by mail. Twelve participants responded. They were mailed several picture fragments; some were from pictures they saw and others were not. There were also two control groups (both had larger sample sizes) of college aged students and age-matched adults. The results were as follows:
Picture fragments corresponding to previously named pictures were identified at a mean rate of 56.0%, and new fragments were identified at a mean rate of 43.5%. The control group—who had seen none of the stimuli previously—identified the two types of fragments at similar levels, 58.1% for targets and 56.5% for foils. Priming—the difference between correct identification rates for old and new fragments—was significantly greater for the longitudinal group (i.e., the original subjects; M = 12.5%) than the control group (M = 1.6%). Virtually all the longitudinal subjects showed priming above zero (11 of 12, or 92%), whereas only 43% (9 of 21) of the control subjects did.
So these participants identified fewer new fragments (due to age-related declines in picture fragment completion tasks) but showed greater benefit from seeing them before (again, 17 years before!). This priming benefit is substantial – I often ask my students if they wouldn’t like to score 12% higher than they do presently. From a few brief exposures and some work with a stimulus we have powerful implicit memory traces that last a lifetime. No wonder we are so subject to déjà vu experiences!