THE SENSES • The process by which physical energy from objects in the world or in the body stimulates the sense organs
Measuring The Senses • Psychologists assess the acuity of the senses in three ways: • Measuring the absolute threshold • Measuring the difference threshold • Applying signal detection theory
Absolute threshold is the minimum amount of stimulation required for a person to detect the stimulus 50% of the time
Difference threshold is the smallest difference in stimulation that can be detected 50% of the time
Researchers use signal detection theory to predict when a weak signal will be detected
Sensory Adaptation • The decrease in sensitivity to an unchanging stimulus
Development of the Senses • Babies have all the basic sensory abilities & many perceptual skills, they develop & grow more sensitive over time
VISION • Has been studied more thoroughly than the other senses • Would not exist without the presence of light • Light is electromagnetic radiation that travels in the form of waves
We experience light as having three features: • Color • Brightness • Saturation
Eye Physiology • The human eye is about one inch in diameter
Structure of the Eye • The cornea is the transparent, protective outer membrane of the eye
The iris surrounds an opening called the pupil, which can get bigger or smaller to allow different amounts of light through the lens to the back of the eye.
The lens, which lies behind the pupil and iris, can adjust its shape to focus light from objects that are near or far away. This process is called accommodation.
Rods and Cones • Rods are sensitive to only degrees of brightness • Rods are specially adapted for sensing stimuli at low levels of light, like at twilight or at night
Rods and Cones • Cones are receptors specialized for seeing color • Cones function only in daylight • In humans, cones cluster around the center of the retina
Optic Disc • Rods and cones connect with bipolar cells, these cells connect with large ganglion cells • The axons of these ganglia are bundled together and leave the retina at the optic disc
Optic Nerve • Each optic nerve can be thought of as two separate bundles corresponding to they receptors in the left and right side of the retina
David Hubel and Torsten Wiesel showed in the 1960s that highly specialized cells, called feature detectors, respond to visual signals in the primary visual cortex
Trichromatic Theory • Thomas Young and Hermann von Helmholtz proposed the trichromatic theory, or Young-Helmholtz theory. • This theory states that the retina contains three types of cones, which respond to light of three different wavelengths, corresponding to red, green, or blue.
The Opponent-Process Theory • Ewald Hering proposed the opponent process theory. • According to this theory, the visual system has receptors that react in opposite ways to three pairs of colors. • The three pairs of colors are red versus green, blue versus yellow, and black versus white.
The ability to see separate objects or forms is essential to daily functioning
Gestalt Psychology • School of thought (Germany – early 20th century), explored how people organize visual information into patterns and forms
Gestalt psychology described several principles we use to make sense of what we see
Binocular cues require both eyes • Help estimate the distance of nearby objects • Retinal disparity & Convergence
Monocular cues require only one eye • Help us estimate the distance of objects: • interposition, motion parallax, relative size & clarity, texture gradient, linear perspective, and light & shadow
Perceptual Constancy • Perceptual constancy also helps us make sense of the world • The ability to recognize that an object remains the same even when it produces different images on the retina • Perceptual constancy relates to the other senses also, but visual constancy is the most studied
Visual Illusions • An illusion is a misrepresentation of a sensory stimulus • Can occur in other senses, but most research has been done on visual illusions
Perceptual Set • Perceptual set is the readiness to see objects in a particular way based on expectations, experiences, emotions, and assumptions
Selective Attention • Selective attention is the ability to focus on some bits of sensory information and ignore others
Loudness • Depends on amplitude, or height, of sound waves
Pitch • Though influenced by amplitude, depends most on frequency of sound waves