How your brain retrieves a memory when you sense something familiar
Several years after graduating, I visited my old university for the first time since leaving. I tried to use the familiar campus ATM, but the PIN I entered was not accepted. It took two failed attempts before I realised that I was entering the PIN I had when I studied there – a PIN I had not used or thought about since my student days.
The influence of the environment on memory is evident in many everyday life experiences. We can all probably think of an example where we revisited a place and memories of events from that period re-emerged. And the effect of environmental context on memory has been demonstrated very often in psychological studies.
A now classic experiment conducted by Godden and Baddeley in 1975 employed divers who encoded (memorised) a list of words either on land or underwater. The divers were then asked to write down as many words as they could remember (known as free recall) while in each environment. As predicted, their performance was best when the encoding and retrieval contexts matched; that is, for example, when they were recalling words on land that they had memorised on land.
While the role of our environment in shaping our memory might seem fairly obvious and intuitive, the picture isn't so clear. How exactly does information peripheral to the event we are attempting to remember, such as a room, a smell, a piece of music or the background colour of a computer screen, contribute to memory retrieval? One answer is via recognition memory.
Recognition memory can be defined as the ability to distinguish between stimuli that were encountered previously (targets) from stimuli that were not (distractors). Until a few years ago, it was frequently assumed that recognition involved a single process based on the match between the stimulus presented and all relevant information in memory (including environmental context) which contributed to a familiarity value. A high enough value would result in a recognition response (correctly or incorrectly): "Yes, this was one of the items I saw earlier."
In the last few years, however, dual-process models of recognition have gained momentum over single process models. These generally assume that two processes are involved in recognition: recollection and familiarity. The difference between the two processes is nicely illustrated in an example by George Mandler:
Consider seeing a man on a bus whom you are sure that you have seen before; you 'know' him in that sense. Such a recognition is usually followed by a search process asking, in effect, where could I know him from? Who is he? The search process generates likely contexts (do I know him from work; is he a movie star; a TV commentator; the milkman?). Eventually, the search may end with the insight. That's the butcher from the supermarket!
So, how does environmental context feature in dual-process recognition? The assumption is that familiarity is a process that is independent of context – in other words, familiarity doesn't rely on your brain retrieving peripheral information – while recollection does depend on context. Indeed, it has been found that only recollection is affected when there's a match or mismatch in the environmental context between encoding and retrieval.
Evidence from neuroimaging has further contributed to our understanding of the mechanisms involved in recognition. On the basis of a review of relevant studies, a group of US researchers constructed the binding of item and context (BIC) model. It postulates that medial temporal lobe regions in the brain – a heavily researched brain area known to be involved in memory processing – have distinct roles when it comes to dual-processing.
One part processes item information (contributing to familiarity), one processes spatial and non-spatial contextual information (the environmental context) and another, the hippocampus, processes item-context associations (contributing to recollection).
However, the studies reviewed by the researchers were based on whether participants could retrieve the environmental context – for example, "Did you see this word earlier, and, if so, was it presented on a green or red background?" – rather than on whether re-exposing them to the environmental context itself helped them to recognise the item – for example by testing word recognition on the same colour background or a different colour background without making explicit reference to the background itself.
There is some evidence to suggest, though, that remembering the environmental context of an event may not be necessary for the context to have an influence on retrieval. For example, one study demonstrated that traumatic brain injury patients with impaired memory often retrieved information better if they were in the same room in which they encoded it.
Such evidence would suggest that it is necessary to investigate the influence of environmental context more thoroughly – especially in terms of any incidental influence it has on retrieval as opposed to whether the environmental context itself can be retrieved or not.
We are still a long way from fully understanding with any confidence the full role that environmental context has in retrieval but when I came unwittingly close to blocking my card with the wrong PIN, it became very clear it can play some fascinating tricks on the mind.