The Neural Basis of Thought and Language Midterm Review Session

DISCLAIMER We haven’t seen the test We don’t know what’s on the test What we present today is purely our opinion on what some of the important topics are

Administrivia Midterm in class next Tuesday, March 7 th Be there on time! Format: –closed books, closed notes –short answers, no blue books –up to Feb. 28 th lecture

The format for this evening... Question Work on it Discuss Repeat...

What’s been covered so far... Learning and Memory Connectionist modeling PDP systems Back-propagation Brain imaging Psycholinguistics Mirror Neurons Color Image Schemas Regier System

Details... Neurobiology/ Chemistry –neural firing –axons, synapses –differences from the computer –spreading activation –triangle node –mutual inhibition –reaction time experiments –neural development –learning / memory Computational Bridge –connectionist modeling –learning Hebbian learning supervised learning unsupervised learning recruitment learning reinforcement learning –neural network feedfoward network recurrent networks –backpropagation algorithm E,  W, , ,  gradient descent (local minimum) shift invariance Cognitive Linguistics –color experiment –categories / prototypes –basic level categories –image schemas –force-dynamics –frames Word Learning –Regier model –structured connectionism –no negative examples

Hebbian Learning How do the strengths of the weights change in Hebbian Learning if the following neurons fire?

Hebb’s Rule: neurons that fire together wire together Long Term Potentiation (LTP) is the biological basis of Hebb’s Rule Calcium channels is the key mechanism LTP and Hebb’s Rule strengthenweaken

Long Term Potentiation (LTP) These changes make each of the winning synapses more potent for an intermediate period, lasting from hours to days (LTP). In addition, repetition of a pattern of successful firing triggers additional chemical changes that lead, in time, to an increase in the number of receptor channels associated with successful synapses - the requisite structural change for long term memory. –There are also related processes for weakening synapses and also for strengthening pairs of synapses that are active at about the same time.

Questions?

Learning What type of learning discussed in class solves the problem of assigning blame?

Back-prop Questions?

The Brain What areas of the brain would be active when picking up an object vs. seeing someone pick up an object? How does this play into the embodiment debate?

The Mirror Circuit in Monkeys top: monkey sees experimenter grasp an object bottom: monkey sees experimenter reaches his hand behind a screen to grasp an object this is what we see in a monkey… measuring a neuron in the parietal area

Somatotopy top: humans watching foot, hand and mouth actions without an object bottom: humans watching same actions with an object What can we learn from these two experiments? integrated, multi-modal representation of actions, along with the objects and locations Buccino et al., 2001

Concepts What Concepts Are: Basic Constraints –Concepts are the elements of reason, and –constitute the meanings of words and linguistic expressions.

Concepts: Traditional Theory The Traditional Theory Reason and language are what distinguish human beings from other animals. Concepts therefore use only human-specific brain mechanisms. Reason is separate from perception and action, and does not make direct use of the sensory-motor system. Concepts must be “disembodied” in this sense.

The neural theory Human concepts are embodied. Many concepts make direct use of the sensory-motor capacities of our body-brain system. Many of these capacities are also present in non-human primates. Let us look at concepts that make use of our sensory-motor capacities, ex. Grasp.

Questions?

Color What is the biological basis of basic color terms?

The WCS Color Chips Basic color terms: –Single word (not blue-green) –Frequently used (not mauve) –Refers primarily to colors (not lime) –Applies to any object (not blonde) FYI: English has 11 basic color terms

Results of Kay’s Color Study If you group languages into the number of basic color terms they have, as the number of color terms increases, additional terms specify focal colors Stage IIIIIIa / IIIbIVVVIVII W or R or YWWWWWW Bk or G or BuR or Y RRRR Bk or G or BuG or BuYYYY BkG or BuGGG BkBu WBk RY+Bk (Brown) YR+W (Pink) Bk or G or BuR + Bu (Purple) R+Y (Orange) B+W (Grey)

Color Opponent Cells These cells are found in the LGN Four color channels: Red, Green, Blue, Yellow R/G, B/Y pairs much like center/surround cells We can use these to determine the visual system’s fundamental hue responses Mean Spikes / Sec Wavelength (mμ) R-G G-R Y-B B-Y (Monkey brain)

Questions?

Categories Internal structure (classical, radial, family resemblance, prototype-based, “essentially- contested,” ad-hoc) “External” structure (basic-level, superordinate, subordinate)

Categories What are super- and sub-ordinate types to “red”?

Categories Furniture SofaDesk leather sofa fabric sofa L-shaped desk Reception disk Basic-Level Category Superordinate Subordinate

Basic-Level Category Perception: –similar overall perceived shape –single mental image –(gestalt perception) –fast identification Function: –general motor program Communication: –shortest –most commonly used –contextually neutral –first to be learned by children –first to enter the lexicon Knowledge Organization: –most attributes of category members stored at this level What constitutes a basic-level category? Red? Maroon? yes arguable (expertise)

Categories: Internal Structure Classical Category: –necessary and sufficient conditions Radial Category: –a central member branching out to less-central and non-central cases –degrees of membership, with extendable boundary Family Resemblance: –every family member looks like some other family member(s) –there is no one property common across all members (e.g. polysemy) Prototype-Based Category Essentially-Contested Category (Gallie, 1956) (e.g. democracy) Ad-hoc Category (e.g. things you can fit inside a shopping bag)

Questions?

Image Schemas and Regier

Image Schemas Trajector / Landmark (asymmetric) –The bike is near the house –? The house is near the bike Boundary / Bounded Region –a bounded region has a closed boundary Topological Relations –Separation, Contact, Overlap, Inclusion, Surround Orientation –Vertical (up/down), Horizontal (left/right, front/back) –Absolute (E, S, W, N) LM TR bounded region boundary