Amnesia

Performance Benefits and Costs in Forced Choice Perceptual Identification in Amnesia: Effects of Prior Exposure and Word Frequency by Keane et al

The functioning of the human memory has remained an interesting subject in the medical and psychology field. Many theories and concepts have been developed concerning this cognitive process. One theory that has almost become a universally accepted fact is the existence of two memory recognition processes; the implicit memory and explicit memory. One memory condition that is proves of existence of these dual memory recognition processes is Amnesia. Amnesia is a term that refers to deficit in memory (Amnesia, 2010).

Memory deficits can occur in many different ways. A comprehensive understanding of this phenomenon requires description of cognitive and neural processes of the memory. However, this memory condition has been linked to the classical dual process of recognition memory; implicit and explicit memory recognition (Hirshman, 2005). Keane, Martin and Verfaellie (2009) in their article Performance Benefits and Costs in Forced Choice Perceptual Identification in Amnesia: Effects of Prior Exposure and Word Frequency, have studied the concept of Amnesia in relation to implicit and explicit memory recognition processes. This paper will focus on their observations.

Keane et al (2009) study entailed testing the existence of multiple mechanisms that determine the memory process. Their study was based on an experiment which involved amnesic individual and a control group made up of non-amnesic individuals. The performance of these two groups in a Forced Choice Perceptual Identification (FCPI) was evaluated. The FCPI task involved flashing words that were similar to studied words and requiring the participants to select a response from two choices provided. The choice responses differ from each other by one letter, for example “stake and stare”.

The procedure is such that, a word is flashed out on a computer screen followed by the two choices which compose of the flashed word and its orthographic mate. Keane et al observed that the control group showed performance benefit and cost with high frequency words and a benefit and cost with low frequency words. Amnesic participants showed benefit but no cost with high frequency words and a benefit and a cost with low frequency words. High frequency word refer to word that the participants come across more frequently while low frequency words refers to words that the participants have least exposure to. This study was based on the theory that, when participants are made to select the response, their accuracy in the old condition will be higher than in the unstudied condition ( a performance benefit) while their accuracy in the lure condition will be lower than that in the unstudied condition ( performance cost).

This theory is explained in two ways. The first is based on the argument that, individuals tend to identify a current stimulus according to a recently encountered stimulus. According to this argument, every word is associated with a mental representation (the counter) that accumulates evidence. When the accumulated evidence by the counter surpasses a certain threshold word identification occurs.

For example, recent encounters with the word (car) will accumulate evidence of that word such that if a degraded word similar to (car) is briefly flashed, the individual is likely to identify that word as (car). An alternative argument states that, word identification is a result of a process that makes an individual select between a familiar word and a non familiar word. For example, if a participant is frequently exposed to the word “stake” and during the experiment the word “stare” is flashed then followed by the choices “stare and stake” , the decision of the participant will be based on which word is familiar rather than which has one of them has just been flashed.

Keane et al (2009) came up with the conclusion that the FCPI tasks signaled the operation of the explicit memory rather than the implicit memory in word identification. Amnesic patients marked with impairment in explicit memory showed performance benefits alone with no cost while the control participants showed performance benefits and costs. Normal participants’ enhanced ability to select the studied alternative reflects their tendency to choose words that they remember from the study list. Implicit memory on the other hand, is related to the sensitivity mechanism in the FCPI. The amnesic patients signaled that, the identification process was enhanced by prior exposure to the word that is to be identified and that its identification is not offset by a performance cost that resembles studied stimuli.

Keane’s study involving word identification by both amnesic and non-amnesic participants has proved existence of two memory identification processes. One process produces a general feeling of familiarity (implicit memory) and the other process produces specific recollection of prior experiences (explicit memory) (Hirshman et al, 2005). Hirshman et al conducted an experiment similar to Keane et al. However, Hirshman study involved Midazolam induced amnesia and entailed testing how explicit memory affect identification of words, an event he refers to as the “mirror effect”. According to Hirshman, explicit memories bring about association of the words to be identified with familiar words leading to accuracy in identification of high frequency words and inaccuracy in identification of low frequency words. The aim of the Midazolam induced amnesia is to block the explicit memory. This study also proves the existence of the two processes as the score of the word identification changed with the inducement of amnesia.

Patients suffering form amnesic syndrome usually exhibit impairment in remembering facts and events. This impaired memory is known as the explicit memory. This category of memory is usually characterized by awareness in an individual that a memory is being retrieved (Voss & Paller, 2008). It is also known as the declarative memory. Implicit memory on the other hand, is a cognitive process that supports memory without the awareness of memory retrieval. Hirshman refers to these processes as the “remember” and the know “processes”. "Remember" responses are said to reflect conscious recollections, while "know" responses are considered to reflect feelings of familiarity. It has been a hard task to differentiate between the operations of these two processes of memory recognition. Various tests have been devised to study the individual operation of these two. The FCPI test by Keane et al (2009) has brought the readers a step closer to understanding the difference between explicit and implicit memories.

Keane et al (2009) word recognition test has proved that there exists a difference on how phenomena are recreated within the human mind. The control group participants in the study, showed a benefit and a cost in high frequency and low frequency words. Both the implicit and explicit memory is optimally functioning in these participants indicating a balance between the recollection memory and the familiarity memory. The participants are able to relate the high frequency word to the words they know from previous reading and hence exhibiting both the benefits and costs. The amnesic patients have their explicit part of the brain impaired and therefore their recollection memories are not functioning optimally. In Keane et al study (2009), the amnesic participants exhibit a benefit score on high frequency words and a cost and benefit score on low frequency words.

Lack of cost scores in the high frequency words implies that absence of explicit memories is giving the participants little to compare the flashed words with and hence the high accuracy of their identification. The cost indicators in the control participants arise from the idea that these participants compare their perception of the flashed words to their previous experiences with similar words, what Hirshman refers to as the “hit and false alarms”. This is further enhanced by the ability of the amnesic participants to eliminate the cost benefit relationship in the high frequency words and their failure to eliminate the cost benefit relationship in the low frequency words. As explained earlier low frequency words are words that participants are least likely to have been exposed to before and therefore there is less possibility of there being explicit memories of the words. Therefore, both the control and amnesic group had to rely on implicit memory on these types of words.

In conclusion, human memory is hypothesized to posses two memory recognition processes; the implicit and the explicit memory. While explicit memory are recollection of what has previous been learnt and is usually conscious, implicit memory entail the feeling of familiarity and is usually unconscious. Understanding the memory process of human being will require in-depth study of the processes of implicit and explicit memory recognition. Keane et al (2009) in their article, Performance Benefits and Costs in Forced Choice Perceptual Identification in Amnesia: Effects of Prior Exposure and Word Frequency, have effectively conducted an experiment to distinguish between the two memory recognition processes.

References

Anonymous (2010). Amnesia. April 11, 2011. Available at http://www.psychology.mcmaster.ca/3vv3/chapter9.htm

Hirshman E. et al (2005). Midazolam Amnesia and Dual- Process Models of the Word-Frequency Mirror Effect. University of Colorado. April 11, 2011. Available at psychology.stanford.edu/~jlm/pdfs/HirshmanJML.doc.

Keane M. Martin E. & Verfaellie (2009). Performance Benefits and Costs in Forced Choice Perceptual Identification in Amnesia: Effects of Prior Exposure and Word Frequency. Journal of Memory and Cognition: 37 (5), 655- 666. Available at http://www.bu.edu/mdrc/PDFs/2009_Keane_MemoryAndCognition.pdf

Voss J & Paller K (2008). Brain Substrate of Implicit and Explicit Memory: The Importance of Concurrently acquired neural signals of both memory types. Neuropsychologia: 46(13): 3021- 3029

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