Understanding Sensory Systems

The Five Senses

• Vision, hearing, touch, taste, and smell are required for our brains to process information about the world.

Sensation vs. Perception

• Sensation is the process of the senses picking up stimuli and transmitting them to the brain. Uninterpreted sensory information.
• Perception is the brain organizing and interpreting sensory information.

What is it like to be a Bat?

• Bats use echolocation to locate objects by reflected sound.
• Most animals have some sensory ability that humans do not.
• Birds navigate using the Earth's magnetic field.
• Mantis shrimp detect polarized light.

Why is Understanding Sensory Systems Important?

• Sensory systems are essential for all cognitive processes.
• Understanding their evolution, development, and function in different species is crucial.
• Sensory systems are the first point of contact between an organism and its environment.

Evolution of Sensory Systems

• Humans have evolved a complex visual system to process visual information.
• Humans see vibrant color, but not UV reflections, which guide insects.
• Humans detect odors, but can't track animals like dogs.
• Human auditory systems are finely tuned to the frequencies of speech.
• Visual information is critical for humans.

Hearing Capability

• Different animals have different ranges of hearing.
• Approximate ranges include:
  • Human: 20 Hz to 20,000 Hz
  • Dogs: 50 Hz to 45,000 Hz
  • Cats: 45 Hz to 85,000 Hz
  • Elephants: 1 Hz to 200,000 Hz

Visual Adaptation

• Animals absorb light of specific wavelengths along the electromagnetic spectrum.
• Humans have pigments to absorb wavelengths between 400-700nm.
• Different animals in different environments exhibit different visual sensitivities.
• Evolution has shaped animals' vision based on their lifestyles.

Eye Placement

• Binocular vision occurs when the two visual fields overlap.
• The brain uses the disparity between the left and right eye to create depth perception.
• Prey animals have laterally placed eyes for a larger field of view but less depth perception.
• Predators have forward-facing eyes for better depth perception but a smaller field of view.
• Horses have laterally placed eyes, and whether or not they can detect depth perception.

Rods, Cones, and Retinal Ganglion Cells

• Rods and cones are photoreceptors in the eye that detect light and color.
• Rods are better for night vision, cones are better for color vision.
• Nocturnal animals have more rods than diurnal animals.
• Rod cells are more sensitive to light.
• Retinal ganglion cells are neurons that are the last stop in the eye.
• The information from the photoreceptors passes to the optic nerve and brain.

Human Vision vs. Dog Vision

• Approximate number of retinal ganglion cells and cones in humans.
• Humans (diurnal): 0.7-1.5 million retinal ganglion cells, 4.6 million cones.

Sensory Adaptation in Closely Related Species

• Snakes detect chemical, visual, and thermal cues.
• Sensitivity depends on preferred prey.
• Western fox snakes respond more to visual cues.

Sensory Drive Hypothesis

• Explains the divergence of sensory abilities between and within species.
• Some species develop different sensory capabilities due to communication needs and habitat changes.

Sensory Bias

• A paradox of the evolution of sensory systems.
• Individuals respond more strongly to exaggerated versions of naturally occurring stimuli.

Sensory Exploitation

• The co-opting of existing sensory signals for a new use.

Development of Sensory Systems

• Hubel & Wiesel's pioneering work on sensory system development, particularly the visual system.
• Sensory deprivation during development can have lasting impacts.
• Sensitive periods exist in development during which sensory experience has a profound impact.

Psychophysics

• The study of the relationship between physical stimuli and the sensations and perceptions they evoke.
• Methods like the method of constant stimuli, method of limits, and adaptive/staircase testing are used to measure sensory thresholds (absolute and difference).

Signal Detection Theory

• Recognizes that detection of a stimulus depends on multiple factors, including the intensity of the signal, the presence of noise, and the individual's criterion.
• Includes outcomes using matrices to categorize signal presence/absence, hit, miss, false alarm, correct rejection.

Weber's Law

• The principle that the just noticeable difference (JND) between two stimuli is a constant proportion of the original stimulus intensity.
• Expressed as ΔI/I = k where ΔI is the JND, I is the intensity of the standard stimulus, and k is the Weber fraction.

Method of Constant Stimuli

• A measurement technique using multiple stimuli intensities at various levels and presented in a random order to determine the detection threshold

Method of Limits

• A measurement technique in which the stimulus intensity is changed incrementally (up or down) to determine the intensity needed to detect a stimulus

Adaptive Testing/Staircase Method

• A measurement technique in which the intensity of a stimulus changes based on a subject's response to help pinpoint the threshold

Dark Adaptation

• The process in which the eyes adapt to low light conditions, characterized by an adjustment to a lower threshold for detecting light.

Transduction

• Process of converting physical energy inputs (such as light or sound) into electrical signals that the nervous system can process.