Recognition memory
Recognition memory, a subcategory of explicit memory, is the ability to recognize previously encountered events, objects, or people. When the previously experienced event is reexperienced, this environmental content is matched to stored memory representations, eliciting matching signals. As first established by psychology experiments in the 1970s, recognition memory for pictures is quite remarkable: humans can remember thousands of images at high accuracy after seeing each only once and only for a few seconds.
Recognition memory can be subdivided into two component processes: recollection and familiarity, sometimes referred to as "remembering" and "knowing", respectively. Recollection is the retrieval of details associated with the previously experienced event. In contrast, familiarity is the feeling that the event was previously experienced, without recollection. Thus, the fundamental distinction between the two processes is that recollection is a slow, controlled search process, whereas familiarity is a fast, automatic process.
Mandler's "Butcher-on-the-bus" example:
Imagine taking a seat on a crowded bus. You look to your left and notice a man. Immediately, you are overcome with this sense that you've seen this man before, but you cannot remember who he is. This automatically elicited feeling is familiarity. While trying to remember who this man is, you begin retrieving specific details about your previous encounter. For example, you might remember that this man handed you a fine chop of meat in the grocery store. Or perhaps you remember him wearing an apron. This search process is recollection.
Historical overview
The phenomenon of familiarity and recognition has long been described in books and poems. Within the field of Psychology, recognition memory was first alluded to by Wilhelm Wundt in his concept of know-againness or assimilation of a former memory image to a new one. The first formal attempt to describe recognition was by the English Doctor Arthur Wigan in his book Duality of the Mind. Here he describes the feelings of familiarity we experience as being due to the brain being a double organ. In essence: we perceive things with one half of our brain, and if they somehow get lost in translation to the other side of the brain, this causes the feeling of recognition when we again see said object, person, etc. However, he incorrectly assumed that these feelings occur only when the mind is exhausted, such as from hunger or lack of sleep. His description, though elementary compared to current knowledge, set the groundwork and sparked interest in this topic for subsequent researchers. Arthur Allin was the first person to publish an article attempting to explicitly define and differentiate between subjective and objective definitions of the experience of recognition, although his findings are based mostly on introspections. Allin corrects Wigan's notion of the exhausted mind by asserting that this half-dream state is not the process of recognition. He briefly refers to the physiological correlates of this mechanism as having to do with the cortex but does not go into detail as to where these substrates are located. His objective explanation of the lack of recognition is when a person observes an object for a second time and experiences the feeling of familiarity that they experienced this object at a previous time. Woodsworth and Margaret and Edward Strong were the first people to experimentally use and record findings employing the delayed matching to sample task to analyze recognition memory. Following this, Benton Underwood was the first person to analyze the concept of recognition errors in relation to words in 1969. He deciphered that these recognition errors occur when words have similar attributes. Next came attempts to determine the upper limits of recognition memory, a task that Standing endeavored. He determined that the capacity for pictures is almost limitless. In 1980 George Mandler introduced the recollection-familiarity distinction, more formally known as the dual process theory.Dual-process versus single-process theories
It is debatable whether familiarity and recollection should be considered as separate categories of recognition memory. This familiarity-recollection distinction is what is called a dual-process model/theory. "Despite the popularity and influence of dual-process theories , they are controversial because of the difficulty in obtaining separate empirical estimates of recollection and familiarity and the greater parsimony associated with single-process theories." A common criticism of dual process models of recognition is that recollection is simply a stronger version of familiarity. Thus, rather than consisting of two separate categories, single-process models regard recognition memory as a continuum ranging from weak memories to strong memories. An account of the history of dual process models since the late 1960s also includes techniques for the measurement of the two processes.Evidence for the single-process view comes from an electrode recording study done on epileptic patients who took an item-recognition task. This study found that hippocampal neurons, regardless of successful recollection, responded to the familiarity of objects. Thus, the hippocampus may not exclusively subserve the recollection process. However, they also found that successful item recognition was not related to whether or not 'familiarity' neurons fired. Therefore, it's not entirely clear which responses relate to successful item recognition. However, one study suggested that hippocampal activation does not necessarily mean that conscious recollection will occur. In this object-scene associative recognition study, hippocampal activation was not related to successful associative recollection; it was only when the prefrontal cortex and the hippocampus were activated that successful performance was observed. Further, eye tracking evidence revealed that participants looked longer at the correct stimulus, and this was related to increases in hippocampal activity. Therefore, the hippocampus may play a role in the recovery of relational information, but it requires concomitant activation with the prefrontal cortex for conscious recollection.
Studies with amnesics do not seem to support the single-process notion. A number of reports feature patients with selective damage to the hippocampus who are impaired only in recollection but not in familiarity, which provides tentative support for dual-process models. Further, a double dissociation between recollection and familiarity has been observed. Patient N.B. had regions of her medial temporal lobes removed, including the perirhinal cortex and entorhinal cortex, but her hippocampus and parahippocampal cortex were spared. She exhibited impaired familiarity but intact recollection processes relative to controls in a yes-no recognition paradigm, and this was elucidated using ROC, RK, and response-deadline procedures. In another study, even when performance between patient N.B. was matched to one amnesic patient who had their hippocampus removed, the double dissociation was still present. While performance was matched post hoc and replication is needed, this evidence rules out the idea that these brain regions are part of a unitary memory strength system. Instead, this double dissociation strongly suggests that distinct brain regions and systems underlie both recollection and familiarity processes.
The dual process theories make it possible to distinguish two types of recognition: first, recognizing THAT one has encountered some object/event before; and second, recognizing WHAT that object/event was. Thus, one may recognize a face, but only later recollect whose face it was. Delayed recognition also shows differences between fast familiarity and slow recollection processes In addition, in the “familiarity” system of recognizing memory two functional subsystems are distinguished: the first one is responsible for recognition of previously presented stimuli and the second one supports recognition of objects as new.
At present, neuroscientific research has not provided a definitive answer to this controversy, although it heavily favors dual-process models. While many studies provide evidence that recollection and familiarity are represented in separate regions of the brain, other studies show that this is not always the case; there may be a great deal of neuroanatomical overlap between the two processes. Despite the fact that familiarity and recollection sometimes activate the same brain regions, they are typically quite distinct functionally.
The question of whether recollection and familiarity exist as two independent categories or along a continuum may ultimately be irrelevant; the bottom line is that the recollection-familiarity distinction has been extremely useful in understanding how recognition memory works.
Measurement and methods
Old-new recognition
This method is used to assess recognition memory based on the pattern of yes-no responses. This is one of the simplest forms of testing for recognition, and is done by giving a participant an item and having them indicate either 'yes' if it is an old item, or 'no' if it is a new item. This method of recognition testing makes the retrieval process easy to record and analyze.Forced choice recognition
In this method, participants are asked to identify which of several items is correct. One of the presented items is the target—a previously presented item. The other items are similar, and act as distractors. This allows the experimenter a degree of manipulation and control in item similarity or item resemblance. This helps provide a better understanding of retrieval, and what kinds of existing knowledge people use to decide based on memory.Use of mental chronometry
When response time is recorded, a faster speed is thought to reflect a simpler process, whereas slower times reflect more complex physiological processes.Hermann von Helmholtz was the first psychologist to inquire whether the velocity of a nerve impulse could be a speed that is measurable. He devised an experimental set-up for measuring psychological processes with a very precise and critical time-scale. The birth of mental chronometry is attributed to an experiment by Helmholtz's colleague, Franciscus Donders. In the experiment, he attached electrodes to both feet of the subject. He then administered a mild shock to either the left or right foot, and told the subject to move the hand on the same side—which turned the stimulus off. In a different condition, the subject was not told which foot the stimulus would act on. The time difference between these conditions was measured as one-fifteenth of a second. This was a significant finding in early experimental psychology, because researchers previously thought that psychological processes were too fast to measure.