Chapter 3 Flashcards
Mental representation
The way in which properties of the outside world are copied/stimulated by cognition.
Neural representation
The way in which properties of the outside world (or of inner events) manifest themselves in the neural signal (e.g. different spiking rates for different stimuli; spike = action potential).
Two main electrophysiological techniques?
(1) Single-cell recording: electrode(s) placed in or near a neuron (invasive), measure number of action potentials per second, (2) electro-encephalography: electrode(s) placed on the skull, measures summed electrical potentials from millions of neurons (sensitive to dendritic currents).
Single-cell recordings proces
(1) Very small electrode implanted into axon (intracellular) or outside axon membrane (extracellular), (2) records neural activity (in other studies also used for stimulation), (3) action potentials of single neurons = basis of neural communication.
Different kinds of neural codes?
(1) Local representation (grandmother cells), (2) fully distributed representation, (3) sparse distributed representation.
Evidence with faces is consistent with (3), possibly a gradual transition to (1) in the hierarchical information processing system.
Grandmother cells
A grandmother cell hypothetically responds to only one stimulus.
Rate coding
Grater rate of response used to code information.
Temporal coding
Greater synchrony of response used to code information (e.g. binding different parts of a line together).
What signal does EEG measure?
Three neurons all firing at a similar rate, but two neurons also fire at the same time (and the other does not), these two neurons can influence each others excitability and hence be said to communicate, if millions of neurons do this then we can observe a wave-like structure at the scalp.
Advantage of EEG
EEG signal is directly related to neural activity (albeit mostly slower dendritic potentials that sum up) and this electrical activity is conducted instantaneously to the scalp. Therefore EEG has an excellent temporal resolution.
Disadvantage of EEG
The EEG signal is derived from different sources in the brain and it is not possible to infer exactly where these sources are from the scalp (inverse problem). Therefore EEG has a poor spatial resolution.
Main uses of EEG in cognitive neuroscience
(1) Rhythmic oscillations and links to cognitive function, (2) event-related potentials (ERPs), (3) representational dynamics = use of multivariate statistics & machine learning to investigate how representations change across time (continuous and more powerful compared to (2).
Oscillation-based analyses
Neurons tend to fire in synchrony with each other, but at different frequencies (slow versus fast). Different oscillation frequencies characterize the different phases of sleep-wake cycle. Different frequencies also characterize certain cognitive functions: increased alpha (7-14 Hz) lined to visual attention and increased gamma (30 Hz+) lined to perceptual grouping.
Event-related potentials
Based on EEG recording, EEG signal is averaged over many events (to reduce effects of random neural firing) and aligned to some aspect of the event (e.g. onset of stimulus, pressing a button), electrodes record a series of positive and negative peaks, timing and amplitude of the peaks is related to different aspects of the stimulus and task (e.g. consider face recognition).
Mental chronometry
Measuring the timing of cognition to infer its structure, classic method is RT to a task/stimuli and measure changes in RT across conditions, attempts to decompose the single measure (e.g. Sternberg), ERP signal is continuous over time and has some advantages over RT time. In ERP, different peaks may approximitely reflect the functioning of different cognitive stages, but not a simple relationship between ERP peak and cognition, because each peak is a sum of different electrical activities.
