Midterm 1

Midterm 1

Oct. 21 in class

Read this article by Wednesday next week!

Cognitive Psychology

• High resolution instrumentation is of no use if you don’t understand the cognitive operations that you are trying to image

• Cognitive psychologists have worked to understand mental operations for over a century

• The enterprise of Cognitive Neuroscience is predicated on cognitive psychology

Temporal and Spatial Resolution are Traded Off

Comparing Imaging Techniques - Advantages

• fMRI– ubiquitous

– high spatial resolution

– non-invasive/safe

• PET– quiet

– labels variety of molecules

• EEG/ERP– inexpensive– high temporal resolution– non-invasive/safe

• MEG– high-temporal resolution– good but limited spatial

resolution– non-invasive/safe

• Unit Recording– very high spatial resolution– high temporal resolution

• Lesions– real-life

Comparing Imaging Techniques - Disadvantages

• fMRI– loud

– expensive

– limited temporal resolution

• PET– very expensive

– limited safety

– invasive

– limited temporal resolution• EEG/ERP

– limited spatial resolution– can be difficult to interpret

• MEG– limited spatial resolution– difficult to interpret

• Unit Recording– very invasive– can be hard to see “big picture”

• Lesions– very invasive

There is no “best” level of explanation

• There is only a level of explanation that is most appropriate for your goals– E.g. cognitive psychologist exploring behavioural treatments

for ADHD vs. Molecular neuroscientist pursuing “rational drug design” for ADHD

Cognitive Operations

• What does the brain actually do?

• Some possible answers:– “The mind”– Information processing…– Transforms of mental representations– Execution of mental representations of actions

First Principles

• “cognitive operations are processes that generate, elaborate upon, or manipulate representations”

– As patterns of activity in one or more neurons– We often lack conscious access to these representations– Neuroscientists still know very little about how information is

represented in the brain

Mental Representations

• Mental representations can start with sensory input and progress to more abstract forms

– Local features such as colors, line orientation, brightness, motion are represented at low levels

How might a neuron “represent” the presence of this line?



– Local features such as colors, line orientation, brightness, motion are represented at low levels

A “labeled line”- Activity on this unit “means” that

a line is present- Does the line actually have to

be present?



– texture defined boundaries are representations arrived at by synthesizing the local texture features


• Mental representations can be “embellished”

- Kaniza Triangle is represented in a way that is quite different from the actual stimulus

-the representation is embellished and extended


• Mental Representations can be transformed

– Rubin Vase, Necker Cube are examples of mental representations that are dynamic



– Shepard & Metzlar (1971) mental rotation is an example of transforming a mental representation in a continuous process

Mentally rotate the images to determine whether they are identical or mirror-reversed

SAME MIRROR-REVERSED




– The time it takes to respond is linearly determined by the number of degrees one has to rotate

– Somehow the brain must perform a set of operations on these representations - where? how?


• Mental Representations can be transformed into abstract information representations

– Posner letter matching task

– Are these letters from the same category (vowels or consonants) or are they different?




– Are these letters from the same category (vowels or consonants) or are they different?

– Are they physically the same or are they the same in an abstract way - they are in the same category?

A A

A a

A U

S C

A S

SAME

DIFFERENT




– Participants are fastest when the response doesn’t require transforming the representation from a direct manifestation of the stimulus into something more abstract


• Mental Representations can interfere

– Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour




RED




BLUE




GREEN




RED




BLUE




GREEN




– The mental representation of the colour and the representation of the text are incongruent and interfere

– one representation must be selected and the other suppressed

– This is one conceptualization of attention


• These are some examples of how a cognitive psychologist might investigate mental representations

• The cognitive neuroscientists asks:

– where are these representations formed?

– What is the neural mechanism? What is the code for a representation?

– What is the neural process by which representations are transformed?

First Principles

• What are some ways that information might be represented by neurons?

First Principles

• What are some ways that information might be represented by neurons?

– Magnitude might be represented by firing rate (e.g. brightness)

– Presence or absence of a feature or piece of information might be represented by whether certain neurons are active or not – the “labeled line” (e.g. color, orientation, pitch)

– Conjunctions of features might be represented by coordinated activity between two such labeled lines

– Binding of component features might be represented by synchronization of units in a network

Midterm 1

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