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The senses are:
Vision is the primary sense in humans. Blindness is a much more serious disability than in any of the other senses. The human also does a lot of analysis of vision. A huge proportion of our brain is devoted to vision.
Perception is very subjective.
Sensation and perception:
E.g.: the human eye is sensitive to only a spectrum of wavelengths.
S&P have evolved to help us survive and reproduce, so they are:
How to study perception experimentally:
Psychological approach:
Just noticeable difference (JND). Depends on the stimulus and the amount of it.
Weber-Fechner law: detectable difference increases with average stimulus intensity. It describes the relationship between a physical intensity and its perceived intensity.
How to determine a perceptual threshold: 2-alternative forced choice. Method of constant stimuli: present trials with extent of differences randomized from one trial to the next. Plot detection probability against extent of difference. Steepest point of curve: largest change to the smallest change in stimulus (75%)
Slope: change from missing to perceiving the difference.
More efficient: make the next trial harder for a correct answer and easier for an incorrect answer.
Biological approach:
These are closely related
Spikes are often seen as the gold standard of neural activity. Spikes are very small changes, so they must be measured directly from the neuron. These recordings are invasive inside the brain of an animal or human.
Measuring synaptic activity:
Oscillations: interaction between excitatory and inhibitory neuron groups.
Why use EEG?
How does MRI work?:
Deoxygenated blood causes signal loss. It affects T2*. Blood response follows neural activity. This overcompensates: it does not compensate accurately.
So oxyhemoglobin concentration increases due to increased blood flow. This reduces the signal loss. This is the BOLD signal:
Neural activity:
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