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November 02 Evo-Devohttp://scienceblogs.com/pharyngula/2006/07/evolution_of_hormone_signaling.php
Diversity itself creates opportunities for specializationThe Modular theory of mind proposed by evolutionary psychology holds that human brains (and, by extention, behavioral and mental traits) are composed of a number of specialized, domain-specific adaptations. That is, the brain is essentially a "Swiss Army knife", with specific tools designed by evolution to cope with specific problems. Theoretically and empirically, there are very good reasons for this. 1. The specificity of environmental problems in the environment of evolutionary adaptedness.( Devrait pas plutôt dire que : Diversity itself creates opportunities for specialization ?) 2. Successful behavioral/mental adaptation requires facultative responses. 3. The neurophysiology of human mental and behavior traits appears to be quite specific. Modularity is not to be confused with a lack of a factor of general intelligence.
Modèle explicatif de la variation des comportements incluant les interractions causales entre les différents niveaux d'organisations Many of you have heard of the Ultimatum Game: The ultimatum game is an experimental economics game in which two parties interact anonymously and only once, so reciprocation is not an issue. The first player proposes how to divide a sum of money with the second party. If the second player rejects this division, neither gets anything. If the second accepts, the first gets his demand and the second gets the rest. In theory a "rational" player should accept whatever is offered when there isn't a repeated iteration. Reality is different. From The Economist: ...Those results recorded, Dr Burnham took saliva samples from all the students and compared the testosterone levels assessed from those samples with decisions made in the one-round game. What does this tell us? That physiological variables which are under biological (and ultimately genetic) control can affect the typical behavior a given individual exhibits, and, that that behavior can vary despite the same inputs across the population. There isn't any one H. economicus, there are many different ways humans interact and their propensity for a particular strategy might be conditional upon biological parameters. But of course this doesn't mean that a given individual practices a fixed strategy even for the same inputs over time, just as strategies are mixed throughout the population so they are often mixed over time for any given individual. There is both population level and temporal variation which must be taken into account here; the flat uniform world of older economic imaginations were painted in shades of gray despite the multi-colored nature of reality. Additionally, as I have noted before, even genetically close groups which are culturally distinct can exhibit wildly different modal responses to these various experimental economic games. This suggests that variation is not just extant on the biological level (e.g., tracking testosterone variation within the population), but also on the cultural level as the social parameters shift and reshape the landscape of gene-environment interaction. In other words, the behavioral economic biases can be likened to norms of response of particular genotypes in various cultural environments. Though the median value may shift, the distribution remains the same (e.g., if a particular individual is high testosterone it is likely that their response to the ultimatum game in one iteration will always lay at one end of the distribution across cultures though the range and shape of the distributions may vary quite a bit). Reality is complex. I'm alluding here to the interaction of genetic parameters with various cultural norms. Additionally, the current work in relation to various small scale societies where the "nominal" sums offered by economists is non-trivial implies that analogical reasoning plays a strong role in determining how the typical individual will respond. It seems that most peoples don't conceive of utility maximization, they simply resort to analogies with transactions in their conventional life which can be mapped onto the games they are being forced to play. So there are innate parameters that result in a central tendency as well as variation, but there are also cultural parameters which modulate the range and constrain the scale, and, these often express themselves general intelligence operating through analogical (as opposed to deductive) reasoning. This turns rationality into a whole new beast altogether, not only is it bounded, it is nearly eviscerated as we understand it. But why this variation in the first place? First, I am implying that the conditional responses that an individual gives has an expectation which is determined in large part by their genetic inheritance. Imagine for example that the ratio of "aggressive" to "passive" responses in a given game that an individual gives over time as a ratio, and that this ratio is placed upon a graph. I suspect that in many cases you would generate some sort of normal distribution (you might have to transform it though). There would be a median modal ratio; there would be those rare players who engage in "fixed" strategies where they were invariant. In this way you can re-conceptualize the behaviors documented in experimental economics as continuous quantitative traits. We know from population genetic theory that such traits have not been subject to powerful directional selection for long periods of time. Otherwise, the underlying genetic variation would have been exhausted as one behavioral morph comes to dominate the population of strategies (the range of basal testosterone should be very small and predominantly environmental/non-heritable). The reality of polymorphism might imply that the "rationality landscape" (to borrow a term) is characterized by multiple optima. Balancing selective forces such as frequency dependence and environmental variation might also result perpetuation of the mix. Layered on top of this evolutionary biological level is the flux of cultural inputs which serves as the background environment in which the predispositions develop into lifelong typical strategies. We've come a long way from reciprocal altruism. Diversité des variations individuelles causée par diversité des pression sélectiveCertainly there are plenty of human universals. But there are plenty of non-universals. We are familiar with the Red Queen hypothesis in relation to our immune systems. This model arose in large part because of the necessity for constant evolution in the forever war with parasites. If humans are a cultural animal par excellence for whom the flexibility of their behavioral toolkit is essential, should it surprise us if frequency dependent evolutionary dynamics result in a large number of morphs constantly cycling? Perhaps H. sapiens is the Environment of evolutionary adaptedness of H. sapiens ? October 29 David Fitzpatrick - Plasticité cérébrale - Dévelopement visuelIn order to determine whether moving visual stimuli were sufficient to induce the emergence of direction-selective responses, the animals were exposed to two "training" stimuli consisting of grating patterns which drifted back and forth across the visual field perpendicular to the orientation of the grating in opposite directions. These stimuli were presented to the ferrets for 5 seconds at a time, with intervals of 10 seconds, for a period of 20 minutes. Subsequently, the activity of primary visual cortical neurons was observed whilst these stimuli were presented again. For the first 8-10 hours of visual stimulation after
this motion training, no changes were observed in the functional
properties of visual cortical neurons. Most neurons were highly
responsive to the orientation of the stimuli, but their selectivity to
the direction in which the stimuli moved was very weak. Later on, small
groups of cells with a preference for one of the two training stimuli
began to emerge. With time, these responses progressively increased, so
that each group became highly tuned to one or the other training
stimuli (see above figure). The number of neurons selective for each
orientation was also found to increase with time. To test whether it was the motion of the training stimuli that induced these changes in activity, the researchers flashed identical gratings in the ferrets' visual fields for brief periods of time. This "flash training" elicited responses in the same cortical neurons, but the responses did not increase with time. Gratings which moved in eight directions that differed from those in the training elicited little response or none at all. This confirmed that the observed emergence of orientation selectivity was indeed due to exposure to the training stimuli. Closer examination of the responses of individual pyramidal neurons in layer 2/3 of the cortex revealed that the preferred direction of motion of each changed over time, so that it became more like the preferences of its neighbours. Prior to training, most of the cells exhibited uncertain or moderate orientation preferences. Upon presentation of the training stimuli, however, the responses of most neurons became more certain, and the neurons segregated into small domains with a preference for one direction or the other. Other interesting functional changes were also observed. Some neurons maintained their initial moderate preference for one direction of movement and later increased their response to it, while others reversed their orientation preference during training. If, for example, a neuron was surrounded by cells with a preference for the opposite direction, it was likely to reverse its own preference so that it matched that of its neighbours. On the other hand, a neuron surrounded by others with the same preference was unlikely to change its own preference during training. This suggests that the functinal grouping of neurons occurs because of some kind of interaction between neighbouring cells during motion training. October 24 Developmental modularity vs Evolutionnary modularityPrécis of Neuroconstructivism: How the Brain Constructs CognitionAnother important implication is the central role of developmental trajectories in the interpretation of adult cognition. There is no teleology involved in development; mature, normative cognition is an outcome of development, not a pre-specified target (Thomas & Karmiloff-Smith 2003). September 20 Theory of concepts
“Conceptual semantics – the language of thought – must be distinct from language itself, or we would have nothing to go on when we debate what our words mean.” Pinker, The stuff of thought, p.4
That's where I differ with Pinker too. Two identical utterances can have different meaning whitout having to posit anything else then the neurological history of each words. September 19 Assignation de fonction suite à une lésion - Distinction entre role cognitif et travail cogntif (cognitive working)http://talkingbrains.blogspot.com/2008/01/semantics-and-brain-more-on-atl-as-hub.html Suppose the evidence does pan out that the ATL is critically involved in the semantic deficits found in semantic dementia. Can we conclude that the architecture in the bottom panel of the above figure is correct? Not necessarily, as pointed out in our class by Mary Louise Kean. Just because a single region is implicated in some function, doesn't mean that computationally that region as a whole performs a single computation function. For example, it could be that the ATL contains parallel circuits (convergence zones, say) each performing a similar integrative function but across their own idiosyncratic domains. The parallel circuits in the basal ganglia are a model for this kind of architecture. ----- As far as modularity goes, there is some. You can predict what kind of deficits a person will have based on where an injury occurs. The problem comes from assuming that this is where the processing of that particular thing is done. To use computers as an analogy - I can't help it - if we cut the power cord on a compter it stops adding numbers together. Thus addition takes place in the power cord. |
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