Monday, February 05, 2007

Emotion and Decision Making

Notes on "Emotion, Decision making and the Orbitofrontal Cortex", A. Bechara, H. Damasio, A. Damasio (2000), Cerebral Cortex, vol 10, p295-307.

The Somatic marker hypothesis (defined by Damasio, 1994 and 1996) says that a defect in emotion and feeling has a detrimental effect on decision making - it also proposes a number of brain structures thought to underlie this effect. Emotions in this theory are defined to be 'somatic states' as they are said to be primarily represented in the brain by "transient changes in the activity pattern of somatosensory structures" ('somatic' essentially refers to the internal environment). This paper looks at this theory, focusing particularly on the role of the orbitofrontal cortex and its interaction with the emotion regions of the brain, in addition to a discussion of the relationship between these two distinct functions (decision making and emotion) and the cognitive function of working memory.

There are four basic assumptions upon which the somatic marker theory is based, which are detailed at the start of the paper. (1) many levels of neural operations are responsible for human reasoning and decision making; (2) all cognitive processes depend upon other, supporting, processes such as attention, working memory and emotion; (3) any reasoning and decision making that occurs relies on the availability of information relevant to the current situation - this information is stored in a 'dispositional' form (i.e. implicit knowledge); (4) knowledge may be categorised in one of four ways: "(a) innate and acquired knowledge concerning bioregulatory processes and body states and action, including those which are mad explicit as emotions; (b) knowledge about entities, facts (e.g. relations, rules), actions and action complexes (stories), which are usually made explicit as images; (c) knowledge about the linkages between (a) and (b) items, as reflected in individual experience; (d) knowledge resulting from the categorisation of items in (a), (b), and (c)." On a side note, point (b) implies the presence of at least pseudo-symbols – a prevalent idea in the cognitive sciences, but one which has been strongly debated.

It is upon these four assumptions that the somatic marker hypothesis is further detailed. The orbitofrontal cortex is recognised to be an essential part of the decision making structures – its supposed function in this regard is to learn associations between the present situation on the one hand (or certain aspects of the sensory situation) and emotional (or other bioregulatory) states on the other. This provides a link between the individuals past emotional experience and the present need to make a decision. The somatic marker hypothesis thus proposes that this central linking of emotion to past experiences reduces the decision making space to enable efficient decision making among those options still available after the ‘pre-filtering’ by emotional processes. It is this process, according to the authors, that allows an animal to make an efficient decision on a short time scale. The rest of the article provides an overview of the evidence supporting this hypothesis, of which I will review briefly only a few points.

Using a gambling task, the Skin Conductance Responses (SCRs) of the subjects was taken during performance. The gambling task involved four decks of cards (A, B, C and D), with associated rewards and punishments (in the form of money), arranged such that the short term rewards from two of the decks of cards (A and B) were high in the short term compared to the other two (decks C and D). However, the second set of two decks of cards had a low associated overall loss, whereas the first two decks had a high loss. Overall, in the long-term, it was better to pick cards from decks C and D. The subjects aim was naturally to make as much money as possible. Four main points arose during these studies. Firstly, patients with ventro-medial prefrontal cortex (VM patients) damage exhibited impairment compared to control subjects, which remained constant over time – which is concurrent with the observation in their everyday lives that they are unable to learn from their previous mistakes. Secondly, biases guide decisions. SCRs of participants showed that a ‘sub-conscious’ and emotion-driven prediction of reward or punishment bias forms which does have an effect on the decisions taken, even prior to the conscious awareness of this. Thirdly, there was a suggestion that risk-taking behaviour, which has in the past been linked to prefrontal cortex damage, is not synonymous with impaired decision making (a dissociation between the two). Finally, and following on from the second point, evidence was presented which showed that the biases do not have to be conscious to strongly influence decision making, as demonstrated by the SCR results.

Based on this preliminary evidence in support of the somatic marker hypothesis, a discussion is presented on the relationship between emotion, memory and decision making – two main points caught my eye. It is known that the memory of facts can be enhanced when learned in association with an emotion – from the point of view of the preceding discussion, a natural question to ask would be is working memory, and other memory processes, distinct from those involved in decision making? The answer, in short, is essentially yes: there is a double dissociation (anatomic and cognitive) between decision making on the one hand (anterior VM region), and working memory on the other (right side dorsal lateral prefrontal cortex). A second pertinent question would be whether the emotion mechanism responsible for the increase in memory capabilities is different from the one which influences decision making. The amygdala is known to be central to the workings of emotional processing, and the question thus becomes whether the processing of the two aforementioned processes be distinguished in the amygdala. The answer again seems to yes: experimental results indicate that VM patients are capable of enhancing working memory with emotional cues/responses, but that decision making is impaired, as discussed previously. The final section of the paper describes preliminary work towards answering some of the questions which have arisen during the research, such as "Why do VM patients fail to generate these biases or emotional signals?". Essentially, the "nature of the mechanism responsible for the failure of VM patients to trigger somatic states when pondering decisions remain unspecified."

Most current theories on decision making postulate that decisions are made on the basis of an assessment of the future benefit of possible future outcomes of executing a particular action – i.e. ‘cold, hard logic’ (my words). Emotion may be listed as a contributing and influencing factor, but it is never central as in the somatic marker hypothesis. To recap, this hypothesis "proposes that individuals make judgements not only by assessing the severity of outcomes and their probability of occurrence, but also and primarily in terms of their emotional quality." The few other theories in which emotion takes a central role in decision making (e.g. that by Rolls) essentially view the body as introducing noise into the decision making processes – the somatic marker hypothesis takes an alternate view that these body signals (bioregulatory signals, including emotions) are essential to the decision making process – the reducing of the decision space as mentioned previously.

The implications of this work for artificial cognitive architectures, and thus also in cognitive robotics, are obvious. The view that emotion is something which is central to decision making, and not just an ‘optional extra’ which may add a little interesting functionality (as it may be seen by some), seems to be put to rest by this work on emotion and decision making in humans. So instead of tacking emotion-like constructs onto already fully formed cognitive architectures, it seems necessary to take this as an initial consideration. The point concerning the reducing of the decision space is a particularly interesting one (as previously raised): could this be a small step towards providing a solution to the frame problem for artificial intelligence, and cognitive robotics?

A reference in the paper to another paper on the influence of emotion on memory, which may be of interest:
Cahill et al. (1995), "The Amygdala and Emotional Memory", Nature, 388, pp295-296.

2 comments:

Johan said...

Great overview of the somatic markers hypothesis. I'm only starting to get into this area myself, so this is quite helpful! Will have to dig out the articles you cite.

Dr. Mezmer said...

Perhaps Damasio's research is not novel after all!

Neal Miller’s Somatic Marker

In 1935, the psychologist and learning theorist Neal Miller conducted the following experiment.

To human subjects he presented in unpredictable order the symbols T (followed by electric shock) and 4 (not followed by shock). The shock was followed by a large galvanic response (GSR) that was soon conditioned not only by seeing the symbol T, but by anticipating it. From this and subsequent experiments Miller concluded that organisms should "behave 'foresightfully' because fear (i.e. anxiety), would be mediated by cues from a distinctive anticipatory goal response." Miller further concluded that the 'learned drive' of fear or anxiety, as marked by the GSR, obeys the same laws as do overt responses".

In other words anticipatory somatic changes mediate not choice, but avoidance, and may be described fully by learning principles.

Compare this experiment to the IGT experiment, where an individual again is confronted with a succession of symbols (in this case, markings on a card), and with unpredictable aversive consequences and similar changes in an equivalent somatic measure, the SCR. In this case the unpredicted aversive consequences were large negative card values occurring from time to time. If it is assumed that unexpected 'bad information' is painful as well, then both experiments assume equivalence.

The difference between both experiments is not in their structure, which are more or less equivalent, but rather in the interpretation of the role of the galvanic skin response as a dependent measure. Specifically, the GSR for the Miller experiment correlated with a subjective response that was interpreted as anxiety or fear. For Damasio, the subjective response to arousal as marked by the SCR was subtler, or a mildly or non aversive ‘gut feeling’. In other words, if one assumes that the level of arousal was higher for Miller’s subjects than Damasio’s, the level of arousal could lead to distinctly different interpretations as to the role of arousal. Thus, it is easy to see how Miller assumed that tension based arousal (or anxiety) mediated avoidance, and why Damasio assumed that arousal mediated choice. In other words, if turning a bad card in the IGT experiment signified not a loss of play money but a loss of real money or a painful shock, then avoidance and not choice would have been a more likely interpretation.

So we are left with the original question: what is the role of autonomic arousal? If arousal is dependent upon learning, as both Miller and Damasio hold, what is its function: avoidance, choice, or some mixture of the two that is dependent upon the level of arousal?

One way to ascertain the role of avoidance is to simply examine whether elevated autonomic arousal occurs under response contingencies that either eliminate the ability to avoid or obviate the need to avoid. If results under a response contingency are all bad and unavoidable, then we have Seligman’s learned helplessness, and if all results are good and thus create no need to avoid, then we have Csikszentmihalyi’s ‘flow’ response. Both are marked by low autonomic arousal as marked by a reduction in SCR and a corresponding lack of reported tension, anxiety, or fear. Thus it may be construed that avoidance is an essential function of autonomic arousal. This of course does not directly challenge Damasio’s position, but raises the avoidance hypothesis front and center as an alternative explanation for his findings.



Source:

Miller, N. E. (1971) Selected Papers, Atherton, Chicago

pp-123-171