Credit: Human Brain
Project
A theory that links
memory encoding to expectations of future relevance may better explain how
human memory works, according to a team of Penn State psychologists.
Modern psychology
posits two major theories to explain the mechanisms of how memories are formed.
The first is object-based encoding, storing all information about an object in
working memory.
The second is feature-based encoding, selectively remembering aspects of an
object. For example, if you watch a group of people playing basketball, under
object-based encoding theory, the brain remembers all aspects of the ball. In
feature-based encoding, the brain remembers that it saw a ball, but may have no
recollection of the color if the color of the ball is an unnecessary feature
according to the task at hand.
The proposed theory, expectancy-based
binding, suggests that subjects can remember features presented in a visual
scene or movie without necessarily remembering which object went with which
feature when it is not necessary to do so.
"The key
discovery was that attending an object for an extended period of time does not
ensure that all of the features of that object will be correctly associated
with it in memory," said Brad Wyble, assistant professor of psychology.
The researchers
tested 60 participants and asked them to watch videos in which two balls were
thrown between multiple people. The first ball thrown was the target ball.
Participants counted the number of times the ball was passed. The second ball
was the distractor ball. Each participant watched 36 trials, recording their
counts of the target ball after each. The balls in each video were red, green,
blue or purple. The researchers reported their results in a recent issue of Cognition.
For the first 31
trials, participants chose only the number of passes made with the target ball.
After the thirty-second trial, a message popped up on the participant's screen
that read, "This is a surprise memory test! Here we test the 'Color' of
the target ball. Press a corresponding number to indicate the 'Color' of the
target ball."
To this question, 37
percent of participants—22 of 60—responded with the incorrect color of the
ball, and 16 of these 22 incorrect responses selected the color of the
distractor ball.
"Participants
have memories of the color of both balls, but those memories aren't attached
specifically to the target ball or the distractor ball," said Hui Chen,
post-doctoral fellow in psychology and first author.
It is statistically
significant that 73 percent of participants responded with the color of the
distractor ball. If participants had no memory of the color of the balls seen
in the video, as feature-based encoding might suggest, then participants would
have chosen the distractor ball only 33 percent of the time when they could not
remember the target ball's color.
Four control trials,
in which participants reported the color of the target ball and number of times
the target ball was passed, followed the trial containing the surprise
question. For these trials, the response error was once again lower. Only 14
percent of participants responded incorrectly in the control trials, as
compared to 37 percent in the surprise trial.
"What we're
showing is that attention is not enough to ensure accurate memory," said
Wyble. "You need some kind of expectation that attributing certain
features to the object is important."
This indicates that
much of what a person can remember is based on their expectation of the
information they will need to recall. Once participants realized they would
need to report the color of the ball, they were able to do so with high
accuracy.
To ensure the results
were robust, the entire experiment was repeated a second time with a new group
of participants. The new experiment replicated the results of the previous
experiment, which provides additional confidence that these surprising memory
failures are a genuine effect.
