Chapter 5 - Sensation and Perception
We experience the world in two distinct phases:
• Sensation- the sense’s organ’s responses to external stimuli and the transmission of
these responses to the brainà light, air vibrations, odors)
• Perception- the processing, organizing, and interpretation of sensory signals; results in
an internal representation of the stimulusà form a conscious experience of the world.
2. Receptors detect stimulus
3. Stimulus is transduced
4. Brain processes and constructs representations.
Stimuli Must be Coded to be Understood by the Brain
• Sensory coding: sensory organs translations of stimuli’s physical properties into neural
impulsesàbrain cannot process raw stimuli must be chemical/electrical signals.
• Transduction: sensory receptors (specialized neurons in the sense organs) pass
impulses to connecting neurons when they receive stimulation.
• Coarse coding: sensory qualities are coded by only a few different types of receptors
each respond to different stimuli
Psychophysics Relates Stimulus to Response
- -Our psychological experiences of stimuli.
• Absolute threshold: minimum intensity of stimulation that must occur before you
experience a sensation.
• Difference Threshold: the just noticeable difference between two stimuli—the minimum
amount of change required for a person to detect a difference.
• Signal detection theory: the idea that the detection of a faint stimulus requires judgment
—it is not an all or none process.
à Hit = participant detects stimulus
à False alarm = detects stimulus that wasn’t there
à Miss = doesn’t detect stimulus
à Correct rejection = doesn’t detect stimulus since it wasn’t there.
- Compare hit rate with false alarm rate to correct bias.
Weber’s Law: the noticeable difference between two stimuli is based on a proportion of
the original stimulus rather than on a fixed amount of difference.
• Response bias: Participants tendency to report detecting signals in an confusing trial.
• Sensory adaptation: decrease in sensitivity to a constant level of stimulation
Taste (Gustation: sense of taste)
• Taste buds: sensory receptors that transduce taste informationàcalled papillae
1. Stimulus à molecules dissolve in fluid on tongue
2. Receptor à papillae transmit signal
3. Pathway to brain à along cranial nerve, through hypothalamus and to other areas
4. Result à perception of whether it is good or bad.
Smell (Olfaction: sense of smell)
• Olfactory Epithelium: thin layer of tissue within nasal cavity, embedded with smell
• Olfactory bulb: brain center for smell, below frontal lobes.
1. Odorants pass into nose+ nasal cavity
2. Receptor à olfactory receptors in OE transmit signal to OB
3. Pathway to brain à along olfactory nerve to areas of cortex and amygdala 4. Result à perception of whether it is good or bad.
Touch (Haptic sense: sense of touch)
1. Stimulus à touch something, skin registers temp and pressure
2. Receptor à temp and pressure receptors in skin transmit
3. Pathway to brain à along trigeminal nerve (above neck) or spinal nerve (below neck) through
thalamus and others
4. Result à know how the touch feels.
Hearing (Audition: sense of sound perception)
Ossicles: three tiny bones, hammer, anvil, and stirrup.
Oval window (membrane of cochlea or inner ear): fluid filled tube shaped like a snail.
1. Stimuli: variations in air pressure produce sound waves that arrive at ear
2. Receptor: move through outer ear and make eardrum vibrate
3. Move through middle ear, causing ossicles to vibrate, this causes oval window to vibrate
4. Pressure waves in inner ear fluid bend hair cells, cause neurons on basilar membrane to
fire neural signals
5. Travel along auditory nerve to auditory cortex
6. Hear sound
- Most important source for knowledge
- Very little of what we call seeing occurs in the eyes, rather it is results from constructive
processes that occur throughout much of the brain
- Light first passes through the cornea à thick, transparent outer layer of the eye
- The cornea focuses incoming light in a process called refraction
- Light rays are bent further in by the lens to form an image in the retina à inner surface
of the back of the eyeball
- The pupil is a small opening in the front of the lens
- To determine how much light enters an eye the pupil contracts or dilates
- The iris determines the eyes color and pupil size
- Accommodation is the process where muscles change the shape of the lens, flattening
to see further objects, thickening to see closer ones
- Neurons fire at a rate and in different combinations to represent the external world (like
Rods and Cones
- Retina has two types of receptor cells:
à Rods are for low levels of illumination and don’t support color
à Cones respond to high levels of illumination, support color
- Photopigments initiate transduction of light waves into electrical neural impulses
- Fovea is the center of the retina where cones are packed
Two Types of Pain
- The brain creates pain because it misinterprets neural activity.
1. Myelinated nerve fibers à respond quickly + sharp localized pain à recoil from harm
2. Non-myelinated fibers à respond slower + dull, slow burning pain à keeps us from using the
affected body parts to aid in recuperation.
Gate Control Theory
- For us to experience pain, pain receptors must be activated and a neural “gate” in the
spinal cord must allow signals throughout the brain.
à 2 areas for pain perception: 1. Responds to the sensory input from the part of the body that is in pain
2. The emotional aspects of pain.
Transmission From the Eye to the Brain
- Ganglion Cells are the first cells in the visual pathway to generate action potentials
- Particular visual neurons respond best to particular colors, shapes, directions
- Receptive Field is the region of visual space to which neurons in the primary visual
cortex are sensitive
- Light directed toward the centre region of an eye cause the cell to become more active,
whereas light directed toward the surrounding region inhibits the cell’s firing
- Lateral Inhibition is the visual process in which adjacent photoreceptors tend to slow
down one another à it emphasizes changes in visual stimuli