sensation perception

© 2004 John Wiley & Sons, Inc.Huffman: PSYCHOLOGY IN ACTION, 7E

Sensation and Perception• Sensation is the process of receiving,

converting, and transmitting information from the outside world.– Sensory organs contain receptors that

transduce sensory energy into nerve impulses that are carried to the brain.

• Top-down processing versus bottom-up processing


Sensation/Perception

• Transduction: sensory receptors convert a physical energy into nerve impulses


Understanding Sensation: Processing

Three Types of Processing:

1. Transduction: converts sensory stimuli into neural impulses that are sent on to the brain

2. Sensory Reduction: filters and analyzes incoming sensations before sending on to the brain

3. Coding: converts particular sensory input into a specific sensation sent to differing parts of the brain


Sensory Thresholds• Psychophysics: testing limits and changes

• Absolute Threshold: smallest amount of a stimulus we can detect

• Difference Threshold: minimal difference needed to detect a a stimulus change; also called the just noticeable difference (JND)

© 2011 The McGraw-Hill Companies, Inc.

Signal Detection Theory


Modification of Sensation

• A key function of sensory systems is to detect change within the environment.– Movement in the peripheral aspects of the eye

may signal food or danger.– Constant pressure of an object on the skin may

not be important.• A stimulus that moves across the skin may be a

snake or a spider.• The skin adapts to constant pressure.


Sensory Adaptation

• Sensory adaptation refers to the fact that repeated or constant stimulation decreases the number of sensory messages sent to the brain, which causes decreased sensation.


Gate-Control Theory of Pain

• Pain sensations are processed and altered by mechanisms within the spinal cord.– Endorphins relieve pain by inhibiting pain

perception.


Vision• External light falls on receptors within the

eye to generate the visual message.

• Light = electromagnetic radiation– Wavelength of light determines color


Physical/Perceptual properties of light


Properties of Light

– wavelength: distance between peaks• perceived as hue• some wavelengths beyond human

sensation

– amplitude: height of wave• perceived as brightness

– purity: mixture of wavelengths• perceived as saturation


Anatomy of the Eye


Glaucoma: Open and Closed Angle


Accommodation

• Accommodation refers to automatic adjustments of the eye, which occurs when muscles change the shape of the lens so that it focuses light on the retina from objects at different distances.– Nearsightedness– Farsightedness


Eye as optical instrumentLight refraction


Three layers of eye


Structure of the Eye: Retina


Structure of the Eye: Retina

Rods– sensitive to even dim light, but not color– function well in low illumination– humans have ≈ 120 million rods

Cones– respond to color– operate best under high illumination– humans have ≈ 6 million cones


Retinal Photoreceptors

• Light passes through the retinal layers to reach the photoreceptors at the inner retinal surface.

• Photoreceptors and bipolar cells conduct potentials to the ganglion cells, which in turn initiate action potentials which are transmitted to the thalamus.


Visual System


Color Perception• Humans are able to discriminate 7 million different hues.• Colors convey important information:

– Ripeness of food– Danger signals

• Trichromatic theory– Eye contains 3 different color sensitive elements

• Blue, green or red elements• Trichromatic theory accounts for color mixing of lights.

• Opponent-Process theory– Visual system is organized into red-green, blue-yellow and

black-white units.• Theory can account for negative color afterimages.


Sensory Coding

• Activation of retinal cells by light results in action potentials that travel along neurons that project to the occipital cortex


Properties of Sound

Wavelength (distance between peaks)

- determines frequency

- perceived as pitch

- some wavelengths cannot be perceived

Amplitude (height of wave)- perceived as loudness

Mixture of Wavelengths; Complex Sounds

- perceived as timbre / tone saturation


Sound Loudness (dB)


Anatomy of the Ear

(Sound Waves)


Cross-section

of cochlea


Theories of Hearing

Place Theory of Pitch Perception– location of stimulation is important– only explains perception of high frequencies

Frequency Theory of Pitch Perception– frequency of nerve firing

• limitations of neuronal firing rate– volley principle

• cell clusters can exceed limitations of firing rate


Hearing Loss

• Conduction deafness: Middle-ear deafness resulting from problems with transferring sound waves to the inner-ear.

• Nerve Deafness: Inner-ear deafness resulting from damage to the cochlea, hair cells, or auditory nerve.


Olfaction• Receptors are embedded in a mucus-coated

membrane called the olfactory epithelium.• When chemical molecules in the air pass

through the nose, the receptors initiate a neural impulse which travels to the olfactory bulb, where most olfactory information is interpreted.

• Lock-and-Key Theory: humans can smell various odors because each three-dimensional odor molecule fits into only one type of receptor.


Gustation

• Taste receptors are located on the tongue and are sensitive to five major tastes: salty, sweet, sour, bitter and umami.

• Taste receptors respond differentially to the varying shapes of food and liquid molecules.


The Body Senses

• Skin Senses: there are three basic skin sensations: touch, temperature, and pain.

• Vestibular Sense: sense of body orientation with respect to gravity and three-dimensional space– The semicircular canals provide the brain with balance

information.

• Kinesthetic Sense: sensory system for body posture, orientation and movement– Kinsethetic receptors are found throughout the muscles,

joints, and tendons of the body.


Perception• Perceptual processes include:

– Selection refers to choosing which of many stimuli that will be processed.

– Organization involves collecting the information into some pattern.

– Interpretation involves understanding the pattern.

• Perceptions can be in error– Illusions are visual stimuli that

are misinterpreted .


Horizontal-Vertical Illusion

WHICH LINE IS LONGER?


Selection

• Selective attention: filtering out and attending only to important sensory messages.

• Feature detectors: specialized cells in the brain that respond only to certain sensory information

• Habituation: tendency of the brain to ignore environmental factors that remain constant


Form Perception

• Gestaltists proposed laws of organization that specify how people perceive form.

• Figure and ground are basic organizational themes for perception.– Figure is perceived as distinct from the

background.– Figure is closer to the viewer than the

background.


Visual Perception: Depth

Monocular Cues – Pictorial Cues

• familiar size• height in the field of view• linear perspective• overlap• shading• texture gradients


Monocular Cues: Shading, Texture Gradient


Monocular Cues: Linear Perspective, Height in Field


Gestalt Organizational Principles


Perceptual Constancies

• Perceptual Constancy is the tendency for the environment to be perceived as remaining the same even with changes in sensory input.– Size constancy– Shape constancy– Color constancy– Brightness constancy


Depth Perception

• Depth perception is the ability to perceive three-dimensional space and to accurately judge distance.

• Binocular cues include retinal disparity and convergence.

• Monocular cues include linear perspective, interposition, relative size, texture gradient, aerial perspective, light and shadow, accommodation and motion parallax.


Interpretation

• Interpretation is influenced by:perceptual adaptation

perceptual set

individual motivation

frame of reference


Subliminal Perception

• Subliminal stimuli are stimuli presented below the threshold of awareness; the effect on behavior is uncertain.


Extrasensory Perception

• ESP refers to the ability to perceive stimuli that are outside the 5 senses– Telepathy: the ability to read minds– Clairvoyance: the ability to perceive objects

or events – Precognition: the ability to predict the future– Psychokinesis: the ability to move objects

sensation perception

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