Unit 2 - Sensation and Perception

Sensation and Perception

• The five senses (vision, hearing, touch, taste, smell) are crucial for processing information about the world.
• Sensation is the process where senses detect stimuli and transmit them to the brain. This information is not interpreted.
• Perception is the interpretation of sensory information by the brain and involves organizing and interpreting sensory information.

Sensation vs. Perception

• Sensation involves sensing a stimulus, while perception involves interpreting it after the stimulus reaches the brain.
• Sensory information is registered in the brain, but not interpreted during sensation, whereas perception actively organizes and interprets the sensory information.

What is it like to be a bat?

• Bats use echolocation, a method of locating objects by reflected sound, to navigate and hunt.
• Echolocation is a sensory ability that most humans do not possess.
• Many animals besides bats use different sensory abilities (e.g., birds use earth's magnetic field, mantis shrimps use polarized light).

Why is understanding sensory systems important?

• Sensory input is fundamental to all cognitive processes.
• The study of sensory systems helps understand their evolution, development, and function.
• Sensory systems are the first point of contact between an organism and its environment.

Evolution of Sensory Systems

• Humans see colors and detect odors, but not to the same extent as animals.
• Specific animals have evolved sensory adaptations for their lifestyle and respective environment (e.g., nocturnal animals have more light-sensitive rods, while other animals have excellent depth perception).
• Animals that hunt (predators) and prey have different types of sensory adaptations in their vision.

Rods and Cones, Retinal Ganglion Cells

• Rods and cones are the photoreceptors.
• Rods provide better night vision.
• Cones provide better colour vision.
• Nocturnal animals tend to have more rods than diurnal animals, but often have poorer colour vision.
• Retinal ganglion cells are neurons that process the information from photoreceptors.

Human vision vs. Dog vision

• These numbers are approximations—reported numbers may differ.
• Humans have roughly 0.7-1.5 million retinal ganglion cells and approximately 4.6 million cones.
• Varying numbers exist in other species.

Sensory Systems-Adaptation

• Sensory abilities can adjust in different environments.
• Sensory development, function, and evolution are crucial to survival and adaptation in their environments.

Sensory Adaptation, Development, and Function

• Sensory systems adapt to survive and use the best possible senses.
• Animals develop their sensory functions and how they function changes.
• Sensory systems generally develop after birth enabling animals to function successfully post-natally.

Sensory Detection

• Sensory detection begins at sense organs (eyes, ears, nose, skin, tongue) containing sensory receptors.
• Sensory receptors transmit information to the central nervous system.
• Signal transduction is the conversion of sensory input into electrical signals that travel through neuronal circuits.

Sensory Processing

• Information from organs is separated by modality (vision, hearing, olfaction, taste) before being sent to the brain.
• This prevents information from mixing or muddling.
• Information is then processed by different brain regions.

Psychophysics

• Psychophysics studies the relationship between physical stimuli and our perception of them.
• It involves quantitatively measuring perception.
• Methods like "Method of Limits", "Method of Constant Stimuli", and "Adaptive Testing/Staircase Procedure" are used to measure absolute and difference thresholds.

Signal Detection Theory

• Recognizes that detecting a stimulus is influenced by both the sensory system's sensitivity and the individual's criteria.
• Includes biases, expectations, and signal presence/absence.
• Accounts for the possibility that a subject may want to be more sensitive in their judgments than is possible (and not accurate).

Other Important Concepts

• Absolute Threshold: The minimum intensity of a stimulus needed for detection 50% of the time.
• Difference Threshold (JND): The smallest detectable difference between two stimuli.
• Weber's Law: The principle that the just noticeable difference of a stimulus is a constant proportion of the original stimulus value.
• Dark Adaptation: The process where the eye's sensitivity to light increases in low-light conditions.