Cours 1 - Introduction

Sensation and Perception Introduction

• Sensation is the ability to detect a stimulus and transform it into a personal experience.
• Perception is the act of giving meaning to detected sensations.
• Scientific methods for studying sensation and perception include:
  • Thresholds (limits of what can be perceived).
  • Scaling (measuring subjective experiences).
  • Signal detection theory (a decision-making model).
  • Sensory neuroscience (the biological basis of sensation).
  • Neuroimaging (brain imaging techniques).
  • Computational models (mathematical models to understand perception).

Plato and the Allegory of the Cave

• Our senses only provide limited, imperfect representations of reality.

Psychophysics and Gustav Fechner

• Gustav Fechner (1801-1887) is considered a founder of psychophysics.
• He studied the relationship between physical stimuli and subjective experiences.
• Fechner's Law describes the relationship between stimulus intensity and subjective perception.

Signal Detection Theory (TDS)

• A psychophysical theory that quantifies observer responses to potentially ambiguous stimuli.
• Describes four possible scenarios in a signal detection experiment: hit (signal present, response yes), miss (signal present, response no), false alarm (no signal, response yes), correct rejection (no signal, response no).
• Sensitivity and criteria are important concepts in this theory.
  • Sensitivity measures how easily an observer can distinguish a signal from noise.
  • Criteria is an internally-set threshold that determines an observer's response.

Sensory Neuroscience and Perception

• Johannes Müller's Doctrine of Specific Nerve Energies states that the nature of a sensation depends on which sensory fibers are stimulated, not how they are stimulated.
• Cranial nerves are part of the peripheral nervous system and transmit sensory and motor information to various body parts.

Santiago Ramón y Cajal

• Ramón y Cajal's detailed drawings of neurons and neuronal structures are important contributions to neuroscience.
• He discovered the synapse, a junction between neurons.
• Neurotransmitters are chemical substances that facilitate communication across synapses.
• Ramón y Cajal received a Nobel Prize.

Neural Transmission - Action Potential

• Action potential is an all-or-none phenomenon for neurons.
• The rate of action potentials indicates the level of neural excitation.
• Action potentials are initiated near the cell body and travel along axons towards axon terminals.
• Action potentials involve sodium (Na⁺) and potassium (K⁺) ions moving in and out of the neuron.

Modern Brain Imaging Techniques

• EEG: Measures electrical activity in the brain using electrodes on the scalp.
• Event-Related Potentials (ERP): A technique isolating brain responses to specific events.
• MEG: Measures magnetic fields generated by brain activity.
• CT (CAT) Scan: Uses x-rays to create cross-sectional images of the brain.
• MRI: Uses powerful magnetic fields and radio waves to create detailed images of the brain's anatomy.
• fMRI: Measures changes in blood flow, reflecting active brain regions.
• PET: Measures metabolic activity in the brain, showing which regions are most active.

Computational Models

• Mathematical and computational models are used to model and predict perceptual phenomena.
• These models simulate psychological and neural processes using a variety of methods and approaches.

Perception - A Pseudo-Paradox

• The perceived world is not necessarily identical to external reality.
• Our sensory system involves simplification, organization, and interpretation of sensory input.