A. J. Marr
The concepts of intrinsic and extrinsic motivation are cardinal concepts in social and humanistic psychology, and represent distinctive mental processes that interact in specific ways that can in turn be observed through observation of individuals in work, school, and other institutionalized settings. Various academic viewpoints posit how intrinsic and extrinsic motivation add to one another or disrupt one another, yet there is still no consensus as to how these motivational events interact, or for that matter what they are. In particular, well-researched ‘meta-analyses’ (Deci et al., 1999; Cameron et al. 2001) that summarize the copious literature on intrinsic and extrinsic motivation have come to starkly different conclusions as to how intrinsic and extrinsic motivating factors influence behavior. Indeed, the literature on this topic, like passages in the Bible, can be quoted to serve one’s purposes. Thus, the literature on intrinsic/extrinsic motivation can be interpreted as supporting the idea that external rewards disrupt intrinsic motivation, boost intrinsic motivation, or have no effect whatsoever.
The resolution to this seemingly eternal conundrum is not served by yet another study, but by recognition of the fact that intrinsic and extrinsic motivational processes represent nothing more than metaphorical artifacts that bear not the slightest similarity to the neural processes that actually govern motivation. In other words, the intrinsic vs. extrinsic motivation controversy is a sham because distinctive intrinsic and extrinsic motivational processes simply do not exist. The metaphorical identification of the facts of human motivation (and presumably, human happiness) with the attainment of mental or physical objects as represented by intrinsic and extrinsic motivators is an overarching premise that has encompassed nearly the whole of western philosophy since the days of the Greeks. It is simple, seemingly effective, and generally matches the facts of behavior as represented by common sense. It is also entirely wrong. Within the last ten years, the neuroscientific analysis of the reward mechanisms in the brain has revealed that an entirely different mechanism underlies reward or reinforcement. In this radical new interpretation of reinforcement, mental or physical objects do not reinforce, but rather the prediction error of the perceptual connotations of physical or mental objects. These connotations may reflect the unpredicted sensory attributes of those objects (e.g. the novelty of listening to a Chopin Etude for the first time), or the unpredicted contingent aspects of those objects (e.g. a last minute field goal that wins a football game). This positive and unexpected prediction error in the timing and quality of an event is scaled to the release of the neuromodulator dopamine, a neurochemical that activates or modulates global states of the brain. Dopamine is responsible for fixing attention, increasing the effectiveness of attention (i.e. increases synaptic interconnections and speed of neural activity), and also bestows an appetitive value on behavior that is often perceived as pleasurable. The fact that the unexpected time and content variability of contingent events is critical to the estimate of the quality of reinforcement means that objects per se do not reinforce, but rather the prediction error and the accompanying neural changes that are denoted by objects.
The concept of reinforcement as reflected in the activity of dopamine neurons represents a particular challenge to the canonical metaphorical representation of a reinforcer or reward as a discrete event that controls or motivates behavior as the consequence of a fixed response pattern or contingency. Rather, discrepancy theories of reinforcement assign reinforcement to the prediction error that derives from an individual’s moment-to-moment perception of prevailing response contingencies. That is, reinforcement is a continuous and not intermittent event, and is relative to the quality of prediction error perceived at any moment in time. This view, which is presently the dominant interpretation of learning in neuroscience proposes (Hollerman and Schultz, 1998) that: "Learning depends on the extent to which behavioral outcomes are different than predicted, being governed by the discrepancy of ‘error’ between outcome and prediction. Outcomes that affect learning in this way are termed ‘reinforcers.’…"Learning proceeds when outcomes occur that are not fully predicted, then slows down as outcomes become increasingly predicted and ends when outcomes are fully predicted." Furthermore, "the magnitude of dopamine responses to reward reflect the degree of reward predictability during individual learning episodes…". A dopaminergic based discrepancy theory was first ventured by Donahoe’s Unified Reinforcement Principle (Donahoe and Palmer, 1993), and the fact that dopamine production co-varies with the quality of prediction error, as well as marks prediction error, impacts not just the quality of reinforcement, but also the attendant quality of subjective experience. In other words, the phenomenology of intrinsically rewarding states, or their subjective feeling, can now be rooted to actual physiological processes that can be simply conceived.
Mind Experiments
Take a simple piecework task, such as pulling a lever many times a minute to stamp out buttons on an assembly line. The reward for performing this task, namely a salary, is wholly predictable in its timing and its amount. However, if the timing of the reward as well as its size radically varied over time, then although the average weekly salary would remain the same, the worker could be rewarded substantially, marginally, or not at all after each lever pull. The latter example, which makes the button machine into a slot machine, will result in the otherwise tired and bored worker becoming suddenly animated, interested, excited, and ironically, indifferent to the reasonable expectation that he or she may likely have a net loss at the end of the week. The manipulation of prediction error alone therefore transforms an onerous ‘extrinsically’ motivated task into a highly desirable ‘intrinsically’ motivated task.
As another example, consider a non-rote task that requires an individual to figure out a puzzle or other problem. The solution for a novel problem-solving task also involves unpredictable prediction errors, when progress towards solving the problem occurs intermittently and surprisingly as different options are considered. If the prediction errors are positive, rapid, and high, then we have a lot of dopamine produced and a corresponding enjoyable, flowing, peak, or otherwise pleasurable experience. Similar activities that involve high, rapid, and positive prediction error are creative, sporting, gaming, or other tasks. (In corroboration of these findings, dopamine has been demonstrated to scale up or down with changes in the probability and importance of expected events (Breiter et al, 2001) and with the frequency of cognitive set shifting between unexpected events, such as in creative behavior (Fried et al. 2001) and video game playing (Koepp et al. 1998).
As a final example, let us consider the exemplar of all intrinsically motivated individuals: Shakespeare. If the fanciful movie ‘Shakespeare in Love’ is to be believed, Shakespeare’s genius was spurred by a confluence of motivators, including girlfriends, competitors, fellow actors and investors, not to mention the approval of the crowd, the Queen, and posterity. It was indeed a volatile matrix of uncertainty that excited the imagination and the pen, giving us a play, ‘Romeo and Juliet’, a sublime mixture of pratfalls and poetry that appealed to crowd and Queen alike. But what indeed motivated Shakespeare, uncertainty or contingency? Simple, remove the uncertainty (but not the contingency) and the edifice collapses, and Shakespeare then knows all the right moves, and would likely become bored to tears. He would be no more inspired than a baseball player who knows the final score beforehand, or a gambler who knows the impending face of each card. Shakespeare in Love would become Shakespeare in Hell, a presumption that has at least literary precedent. (See note below for some of the circumstances of the real Shakespeare)
In an episode of the classic TV series ‘The Twilight Zone’, a burglar gets shot and killed, and is met by a jovial fellow who introduces him to a world where he can have anything he wants, from women to power to fame. Unfortunately, everything is totally predictable, from the role of a die to a woman’s sigh. He protests that everything has become boring and dull, and requests to be shipped off to hell, where at least he could play chess with the devil. The man laughs, and says to the shocked burglar, "What made you ever think that you were in heaven?"
Extrinsic and Indivisible for All!
As was previously stated, in contrast to the implicit view that an extrinsic reward is an indivisible event, a discrepancy theory of reward holds that the prediction error signified by 'extrinsic' or objectified reinforcing events is not integral to or fixed by objects, but is dependent upon individual discriminative contexts and histories. For example, although a monetary reward signifies all the things you can imagine you can now buy, which is of course a positive prediction error, that same reward may also signify negative prediction errors as well that are dependent upon contextual cues deriving from present and historical (learning history) events. The well cited example of children losing interest in activities because of a reward is a case in point. If I were to receive a $500 reward for drinking Pepsi, the informative context of the Pepsi and not the Pepsi itself would produce a negative prediction error (is this Pepsi ok to drink?). However, the same $500 reward given for an athletic or creative (e.g. winning the Super Bowl, or a piano competition) accomplishment would likely not result in a negative prediction error, since tradition dictates monetary reward as a validation for and not denigration of accomplishment. Indeed, in such cases, the absence of a monetary reward would likely signal negative prediction error, as it would signify that such accomplishment is taken lightly by society.
Prediction error is dependent upon information that is mediated by the reward, the performance, the environmental context of the behavior, and how it is interpreted due to the personal history of the individual. Unfortunately, because of the near exclusive use by social psychologists of ‘between group’ experimental designs that statistically compare groups of individuals, idiosyncratically perceived informative events are averaged across individuals, and this important data is lost. Hence, the very methodology used by social psychology engenders a self-fulfilling prophecy. By blurring the individual and salient aspects of an individual's experience, homogenized individual variations in behavior are instead relegated to ad hoc motivational causes such as self-actualization, psychic energy, needs for achievement, and of course, intrinsic motivation that have reality only in the imagination.
The unsociable implications for social Psychologists
Social and humanistic psychologists have a penchant for deriving ever-new motivational constructs, from flow states to extrinsic/intrinsic motivation that presumably reflect unique mental processes. In contrast to this top down approach that starts with hypothetical or inferred molar motivational events, a bottoms up approach that begins with real or observed molecular motivational events can remarkably constrain the promiscuous theorizing of unique motivational states that has served to obfuscate much of the science of psychology. The unified principle of reinforcement that is emerging from neuroscience casts doubt on many widely accepted categories of motivation due to the simple fact that they have no distinctive neural correlates, and can be more parsimoniously explained as the emergent properties of very simple neural processes that underlie all behavior. Thus there is no such thing as distinctive intrinsic and extrinsic, operant or respondent, spiritual or materialistic motivating systems. Likewise, there are no distinctive flow states, peak experiences, needs for achievement, or other compartmentalized motivational processes.
Neuroscience has the capability to remove much of the conceptual clutter of psychology, but careers and egos hinge on such theoretical flotsam. Whether of not psychologists have the courage to prune their copious and confusing subject matter will determine if they can actually address the pressing issues that confront society, or if they are merely condemned to debate into infinity and beyond such simple matters as the efficacy of giving gold stars to children. (And of course all this gives wonderful grist for satire, to which I am personally thankful).
Note: (Oh yes. And the real Shakespeare? Consider an environment full of external motivators for a pastime as addictive to its age as our time is for television. To quote Daniel Boorstin’s book ‘The Creators’ (pp.307-310): "The theater had risen in London during Shakespeare’s youth. "The suddenness with which the new pastime had appeared raised the alarm of the learned and the pious. Like television in our time, theater acquired its frightening popularity within a half century." "…..In two weeks during the 1596 season a Londoner could have seen eleven performances of ten different plays at one playhouse, and on no day would he have had to see a repeat performance of the day before."…."Of the twelve hundred plays offered in London theaters in the half century before 1590, some nine hundred were the work of about fifty professional playwrights." (It should be noted that the London of 1590 had about the population of present day Jackson, Mississippi!!) This author wonders what a Vesuvius of inspiration would follow if present day authors had such willing ears, and what any of us would trade for such extrinsic motivation!)
Bibliography:
There are three major sources of information on unified reinforcement or discrepancy theory, and one that is a bit odd.
The first represents the work of the bio-behaviorists John Donahoe and David Palmer. Their Unified Principle of Reinforcement is the first systematic presentation of a discrepancy theory of reinforcement, and scholarly articles on their work can be found on the web site of the Journal of the Experimental Analysis of Behavior (JEAB).
The most lucid and up to date accounts of discrepancy theory are also found on the web. The Google web directory contains quite a few PDF files on articles by the neuroscientist Wolfram Schultz that are lucid yet rigorously argued. Schultz is presently the major figure in neuroscience who has comprehensively examined the neuro-psychology of reward.
The third major source of information on unified reinforcement theory is found in the 1998 book, ‘Affective Neuroscience’, by the distinguished neuro-psychologist Jaak Panksepp. Panksepp is also well represented in the web. His comment (from chapter 8 of his book) is instructive as to the untenability of the concept ‘extrinsic reward’. "From the behaviorist perspective, the incentive properties of a reward were traditionally defined in terms of attributes such as the quality, quantity, and delay of reward rather than in terms of any conception of what the nervous system experiences and undergoes when it is confronted by highly desirable objects. In fact, the high incentive state, from the nervous system perspective, may be the arousal of an emotive process that invigorates search and foraging behaviors. In other words, the unconditional incentive state within the brain may largely consist of the arousal of a psycho-behavioral integrative system (e.g., seeking) of the brain. An increased number of studies measuring DA (dopaminergic) cellular activity, as well as dopamine release in the pathways emanating from the VTA (e.g. a midbrain structure-my note), now indicate that this system is highly tuned to stimuli that predict rewards, rather than to rewards themselves."
Also, the superb web site of the behavioral neuroscientist Kent Berridge is strongly recommended as a primer on incentive motivation processes as instantiated in the human brain.
References:
Breiter, H. C., Aharon, I. Kahneman, D., Anders, Dale, and Shizgal, Peter (2001) functional imaging of neural responses to expectancy and experience of monetary gains and Losses, Neuron, 30, 619-639
Cameron, Judy, Banko, Katherine M, and Pierce, W. D. (2001) Pervasive negative effects of rewards on intrinsic motivation: the myth continues, The Behavior Analyst, (24), 1-44 (article is available entire at behavior.org)
Deci, E. L., Koestner, R., and Ryan, R. M. (1999) A meta-analytic review of experiments examining the effects of extrinsic rewards on intrinsic motivation, Psychological Bulletin, 125, 627-668.
Donahoe, J.W. and D. C. Palmer (1993). Learning and Complex Behavior, Allyn and Bacon
Fried, Itzhak, Wilson, C. L, Morrow, J. W., Cameron, K. A., Behnke, E. D., Ackerson, L. C. and Maidment, N. T. (2001) Increased dopamine release in the human amygdala during performance of cognitive tasks, Nature Neuroscience, 4(2): 201-206
Hollerman, Jeffrey R., and Wolfram Schultz (1998) Dopamine neurons report an error in the temporal prediction of reward during learning, Nature Neuroscience, 1(4): 304-309
Koepp, M.J., Gunn, R.N., Lawrence, A.D., Cunningham, V.J. Dagher, A. Jones, T., Brooks, D.J. Bench C. J., Grasby, P.M. (1998). Evidence for striatal dopamine release during a video game. Nature, 393: 266-268
The resolution to this seemingly eternal conundrum is not served by yet another study, but by recognition of the fact that intrinsic and extrinsic motivational processes represent nothing more than metaphorical artifacts that bear not the slightest similarity to the neural processes that actually govern motivation. In other words, the intrinsic vs. extrinsic motivation controversy is a sham because distinctive intrinsic and extrinsic motivational processes simply do not exist. The metaphorical identification of the facts of human motivation (and presumably, human happiness) with the attainment of mental or physical objects as represented by intrinsic and extrinsic motivators is an overarching premise that has encompassed nearly the whole of western philosophy since the days of the Greeks. It is simple, seemingly effective, and generally matches the facts of behavior as represented by common sense. It is also entirely wrong. Within the last ten years, the neuroscientific analysis of the reward mechanisms in the brain has revealed that an entirely different mechanism underlies reward or reinforcement. In this radical new interpretation of reinforcement, mental or physical objects do not reinforce, but rather the prediction error of the perceptual connotations of physical or mental objects. These connotations may reflect the unpredicted sensory attributes of those objects (e.g. the novelty of listening to a Chopin Etude for the first time), or the unpredicted contingent aspects of those objects (e.g. a last minute field goal that wins a football game). This positive and unexpected prediction error in the timing and quality of an event is scaled to the release of the neuromodulator dopamine, a neurochemical that activates or modulates global states of the brain. Dopamine is responsible for fixing attention, increasing the effectiveness of attention (i.e. increases synaptic interconnections and speed of neural activity), and also bestows an appetitive value on behavior that is often perceived as pleasurable. The fact that the unexpected time and content variability of contingent events is critical to the estimate of the quality of reinforcement means that objects per se do not reinforce, but rather the prediction error and the accompanying neural changes that are denoted by objects.
The concept of reinforcement as reflected in the activity of dopamine neurons represents a particular challenge to the canonical metaphorical representation of a reinforcer or reward as a discrete event that controls or motivates behavior as the consequence of a fixed response pattern or contingency. Rather, discrepancy theories of reinforcement assign reinforcement to the prediction error that derives from an individual’s moment-to-moment perception of prevailing response contingencies. That is, reinforcement is a continuous and not intermittent event, and is relative to the quality of prediction error perceived at any moment in time. This view, which is presently the dominant interpretation of learning in neuroscience proposes (Hollerman and Schultz, 1998) that: "Learning depends on the extent to which behavioral outcomes are different than predicted, being governed by the discrepancy of ‘error’ between outcome and prediction. Outcomes that affect learning in this way are termed ‘reinforcers.’…"Learning proceeds when outcomes occur that are not fully predicted, then slows down as outcomes become increasingly predicted and ends when outcomes are fully predicted." Furthermore, "the magnitude of dopamine responses to reward reflect the degree of reward predictability during individual learning episodes…". A dopaminergic based discrepancy theory was first ventured by Donahoe’s Unified Reinforcement Principle (Donahoe and Palmer, 1993), and the fact that dopamine production co-varies with the quality of prediction error, as well as marks prediction error, impacts not just the quality of reinforcement, but also the attendant quality of subjective experience. In other words, the phenomenology of intrinsically rewarding states, or their subjective feeling, can now be rooted to actual physiological processes that can be simply conceived.
Mind Experiments
Take a simple piecework task, such as pulling a lever many times a minute to stamp out buttons on an assembly line. The reward for performing this task, namely a salary, is wholly predictable in its timing and its amount. However, if the timing of the reward as well as its size radically varied over time, then although the average weekly salary would remain the same, the worker could be rewarded substantially, marginally, or not at all after each lever pull. The latter example, which makes the button machine into a slot machine, will result in the otherwise tired and bored worker becoming suddenly animated, interested, excited, and ironically, indifferent to the reasonable expectation that he or she may likely have a net loss at the end of the week. The manipulation of prediction error alone therefore transforms an onerous ‘extrinsically’ motivated task into a highly desirable ‘intrinsically’ motivated task.
As another example, consider a non-rote task that requires an individual to figure out a puzzle or other problem. The solution for a novel problem-solving task also involves unpredictable prediction errors, when progress towards solving the problem occurs intermittently and surprisingly as different options are considered. If the prediction errors are positive, rapid, and high, then we have a lot of dopamine produced and a corresponding enjoyable, flowing, peak, or otherwise pleasurable experience. Similar activities that involve high, rapid, and positive prediction error are creative, sporting, gaming, or other tasks. (In corroboration of these findings, dopamine has been demonstrated to scale up or down with changes in the probability and importance of expected events (Breiter et al, 2001) and with the frequency of cognitive set shifting between unexpected events, such as in creative behavior (Fried et al. 2001) and video game playing (Koepp et al. 1998).
As a final example, let us consider the exemplar of all intrinsically motivated individuals: Shakespeare. If the fanciful movie ‘Shakespeare in Love’ is to be believed, Shakespeare’s genius was spurred by a confluence of motivators, including girlfriends, competitors, fellow actors and investors, not to mention the approval of the crowd, the Queen, and posterity. It was indeed a volatile matrix of uncertainty that excited the imagination and the pen, giving us a play, ‘Romeo and Juliet’, a sublime mixture of pratfalls and poetry that appealed to crowd and Queen alike. But what indeed motivated Shakespeare, uncertainty or contingency? Simple, remove the uncertainty (but not the contingency) and the edifice collapses, and Shakespeare then knows all the right moves, and would likely become bored to tears. He would be no more inspired than a baseball player who knows the final score beforehand, or a gambler who knows the impending face of each card. Shakespeare in Love would become Shakespeare in Hell, a presumption that has at least literary precedent. (See note below for some of the circumstances of the real Shakespeare)
In an episode of the classic TV series ‘The Twilight Zone’, a burglar gets shot and killed, and is met by a jovial fellow who introduces him to a world where he can have anything he wants, from women to power to fame. Unfortunately, everything is totally predictable, from the role of a die to a woman’s sigh. He protests that everything has become boring and dull, and requests to be shipped off to hell, where at least he could play chess with the devil. The man laughs, and says to the shocked burglar, "What made you ever think that you were in heaven?"
Extrinsic and Indivisible for All!
As was previously stated, in contrast to the implicit view that an extrinsic reward is an indivisible event, a discrepancy theory of reward holds that the prediction error signified by 'extrinsic' or objectified reinforcing events is not integral to or fixed by objects, but is dependent upon individual discriminative contexts and histories. For example, although a monetary reward signifies all the things you can imagine you can now buy, which is of course a positive prediction error, that same reward may also signify negative prediction errors as well that are dependent upon contextual cues deriving from present and historical (learning history) events. The well cited example of children losing interest in activities because of a reward is a case in point. If I were to receive a $500 reward for drinking Pepsi, the informative context of the Pepsi and not the Pepsi itself would produce a negative prediction error (is this Pepsi ok to drink?). However, the same $500 reward given for an athletic or creative (e.g. winning the Super Bowl, or a piano competition) accomplishment would likely not result in a negative prediction error, since tradition dictates monetary reward as a validation for and not denigration of accomplishment. Indeed, in such cases, the absence of a monetary reward would likely signal negative prediction error, as it would signify that such accomplishment is taken lightly by society.
Prediction error is dependent upon information that is mediated by the reward, the performance, the environmental context of the behavior, and how it is interpreted due to the personal history of the individual. Unfortunately, because of the near exclusive use by social psychologists of ‘between group’ experimental designs that statistically compare groups of individuals, idiosyncratically perceived informative events are averaged across individuals, and this important data is lost. Hence, the very methodology used by social psychology engenders a self-fulfilling prophecy. By blurring the individual and salient aspects of an individual's experience, homogenized individual variations in behavior are instead relegated to ad hoc motivational causes such as self-actualization, psychic energy, needs for achievement, and of course, intrinsic motivation that have reality only in the imagination.
The unsociable implications for social Psychologists
Social and humanistic psychologists have a penchant for deriving ever-new motivational constructs, from flow states to extrinsic/intrinsic motivation that presumably reflect unique mental processes. In contrast to this top down approach that starts with hypothetical or inferred molar motivational events, a bottoms up approach that begins with real or observed molecular motivational events can remarkably constrain the promiscuous theorizing of unique motivational states that has served to obfuscate much of the science of psychology. The unified principle of reinforcement that is emerging from neuroscience casts doubt on many widely accepted categories of motivation due to the simple fact that they have no distinctive neural correlates, and can be more parsimoniously explained as the emergent properties of very simple neural processes that underlie all behavior. Thus there is no such thing as distinctive intrinsic and extrinsic, operant or respondent, spiritual or materialistic motivating systems. Likewise, there are no distinctive flow states, peak experiences, needs for achievement, or other compartmentalized motivational processes.
Neuroscience has the capability to remove much of the conceptual clutter of psychology, but careers and egos hinge on such theoretical flotsam. Whether of not psychologists have the courage to prune their copious and confusing subject matter will determine if they can actually address the pressing issues that confront society, or if they are merely condemned to debate into infinity and beyond such simple matters as the efficacy of giving gold stars to children. (And of course all this gives wonderful grist for satire, to which I am personally thankful).
Note: (Oh yes. And the real Shakespeare? Consider an environment full of external motivators for a pastime as addictive to its age as our time is for television. To quote Daniel Boorstin’s book ‘The Creators’ (pp.307-310): "The theater had risen in London during Shakespeare’s youth. "The suddenness with which the new pastime had appeared raised the alarm of the learned and the pious. Like television in our time, theater acquired its frightening popularity within a half century." "…..In two weeks during the 1596 season a Londoner could have seen eleven performances of ten different plays at one playhouse, and on no day would he have had to see a repeat performance of the day before."…."Of the twelve hundred plays offered in London theaters in the half century before 1590, some nine hundred were the work of about fifty professional playwrights." (It should be noted that the London of 1590 had about the population of present day Jackson, Mississippi!!) This author wonders what a Vesuvius of inspiration would follow if present day authors had such willing ears, and what any of us would trade for such extrinsic motivation!)
Bibliography:
There are three major sources of information on unified reinforcement or discrepancy theory, and one that is a bit odd.
The first represents the work of the bio-behaviorists John Donahoe and David Palmer. Their Unified Principle of Reinforcement is the first systematic presentation of a discrepancy theory of reinforcement, and scholarly articles on their work can be found on the web site of the Journal of the Experimental Analysis of Behavior (JEAB).
The most lucid and up to date accounts of discrepancy theory are also found on the web. The Google web directory contains quite a few PDF files on articles by the neuroscientist Wolfram Schultz that are lucid yet rigorously argued. Schultz is presently the major figure in neuroscience who has comprehensively examined the neuro-psychology of reward.
The third major source of information on unified reinforcement theory is found in the 1998 book, ‘Affective Neuroscience’, by the distinguished neuro-psychologist Jaak Panksepp. Panksepp is also well represented in the web. His comment (from chapter 8 of his book) is instructive as to the untenability of the concept ‘extrinsic reward’. "From the behaviorist perspective, the incentive properties of a reward were traditionally defined in terms of attributes such as the quality, quantity, and delay of reward rather than in terms of any conception of what the nervous system experiences and undergoes when it is confronted by highly desirable objects. In fact, the high incentive state, from the nervous system perspective, may be the arousal of an emotive process that invigorates search and foraging behaviors. In other words, the unconditional incentive state within the brain may largely consist of the arousal of a psycho-behavioral integrative system (e.g., seeking) of the brain. An increased number of studies measuring DA (dopaminergic) cellular activity, as well as dopamine release in the pathways emanating from the VTA (e.g. a midbrain structure-my note), now indicate that this system is highly tuned to stimuli that predict rewards, rather than to rewards themselves."
Also, the superb web site of the behavioral neuroscientist Kent Berridge is strongly recommended as a primer on incentive motivation processes as instantiated in the human brain.
References:
Breiter, H. C., Aharon, I. Kahneman, D., Anders, Dale, and Shizgal, Peter (2001) functional imaging of neural responses to expectancy and experience of monetary gains and Losses, Neuron, 30, 619-639
Cameron, Judy, Banko, Katherine M, and Pierce, W. D. (2001) Pervasive negative effects of rewards on intrinsic motivation: the myth continues, The Behavior Analyst, (24), 1-44 (article is available entire at behavior.org)
Deci, E. L., Koestner, R., and Ryan, R. M. (1999) A meta-analytic review of experiments examining the effects of extrinsic rewards on intrinsic motivation, Psychological Bulletin, 125, 627-668.
Donahoe, J.W. and D. C. Palmer (1993). Learning and Complex Behavior, Allyn and Bacon
Fried, Itzhak, Wilson, C. L, Morrow, J. W., Cameron, K. A., Behnke, E. D., Ackerson, L. C. and Maidment, N. T. (2001) Increased dopamine release in the human amygdala during performance of cognitive tasks, Nature Neuroscience, 4(2): 201-206
Hollerman, Jeffrey R., and Wolfram Schultz (1998) Dopamine neurons report an error in the temporal prediction of reward during learning, Nature Neuroscience, 1(4): 304-309
Koepp, M.J., Gunn, R.N., Lawrence, A.D., Cunningham, V.J. Dagher, A. Jones, T., Brooks, D.J. Bench C. J., Grasby, P.M. (1998). Evidence for striatal dopamine release during a video game. Nature, 393: 266-268
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