Writing Workshop

• Find the relevant literature– Use the review journals as a first approach e.g.

• Nature Reviews Neuroscience• Trends in Neuroscience• Trends in Cognitive Science

Writing Workshop

• Pick one theory

Writing Workshop

• Pick one experiment

Writing Workshop

• Pick one technique

Writing Workshop

• Describe experimental design

Binocular Rivalry

• What would happen if each eye receives incompatible input?

Left Eye Right Eye

Binocular Rivalry

• Percept alternates randomly (not regularly) between dominance and suppression - on the order of seconds– What factors affect dominance and suppression?– Several features tend to increase the time one image is

dominant (visible)• Higher contrast• Brighter• Motion

• What are the neural correlates of Rivalry?

Neural Correlates of Rivalry

• What Brain areas “experience” rivalry?• Clever fMRI experiment by Tong et al. (1998)

– Exploit preferential responses by different regions– Present faces and buildings in alternation

Neural Correlates of Rivalry

• What Brain areas “experience” rivalry?• Clever fMRI experiment by Tong et al. (1998)

– Exploit preferential responses by different regions– Present faces to one eye and buildings to the other

Neural Correlates of Rivalry

• What Brain areas “experience” rivalry?• Apparently activity in areas in ventral pathway

correlates with awareness• But at what stage is rivalry first manifested?• For the answer we need to look to single-cell

recording

Neural Correlates of Rivalry

• Neurophysiology of Rivalry– Monkey is trained to indicate

which of two images it is perceiving (by pressing a lever)

– One stimulus contains features to which a given recorded neuron is “tuned”, the other does not

– What happens to neurons when their preferred stimulus is present but suppressed?

Neural Correlates of Rivalry

• The theory is that Neurons in the LGN mediate Rivalry

Neural Correlates of Rivalry

• The theory is that Neurons in the LGN mediate Rivalry

• NO – cells in LGN respond similarly regardless of whether their input is suppressed or dominant

Neural Correlates of Rivalry

• V1? V4? V5?• YES – cells in primary and early extra-striate cortex

respond with more action potentials when their preferred stimulus is dominant relative to when it is suppressed

• However,– Changes are small– Cells never stop firing altogether

Neural Correlates of Rivalry

• Inferior Temporal Cortex (Ventral Pathway)?

• YES – cells in IT are strongly correlated with percept

Neural Correlates of Rivalry

• Inferior Temporal Cortex (Ventral Pathway)?

• YES – cells in IT are strongly correlated with percept• Why does area IT sound familiar to you?

Neural Mechanisms of Consciousness?

• So how far does that get us?

• Not all that far – we still don’t know what is the mechanism that causes consciousness

• But we do know that it is probably distributed rather than at one locus

• Thus the question is: what is special about the activity of networks of neurons that gives rise to consciousness? – that’s still a very hard problem