Psych Chapter 4
• Psychophysics: Basic Concepts and Issues
o Thresholds: Looking for Limits
o Weighing the Differences: The JND
o Psychophysical Scaling
o Signal-Detection Theory
o Perception without Awareness
o Sensory Adaptation
• Our Sense of Sigh: The Visual System
o The Stimulus: Light
o The Eye: A Living Optical Instrument
o The Retina: The Brain’s Envoy in the Eye
o Vision and the Brain
o Viewing the World in Colour
o Perceiving Forms, Patterns, and Objects
o Perceiving Depth or Distance
o Perceptual Constancies in Vision
o The Power of Misleading Cues: Optical Illusions
o Vision for Perception and Vision for Actions
• Our Sense of Hearing: The Auditory System
o The Stimulus: Sound
o Human Hearing Capacities
o Sensory Processing in the Ear.
o Auditory Perception: Theories of Hearing
www.notesolution.com o Place Theory
o Auditory Localization: Perceiving Sources of Sound
o Music and Its Effects
• Our Chemical Senses: Taste and Smell
o Taste: The Gustatory System
o Smell: The Olfactory System
• Our Sense of Touch: Sensory Systems in the Skin
o Feeling Pressure
o Feeling Pain
• Our Other Senses:
o The Kinaesthetic System
o The Vestibular System
Psychophysics – Study of how physical stimuli are translated into
Sensation is the stimulation of sense organs.
Perception is the selection, organization, and interpretation of sensory
Thresholds: Looking for Limits
• Sensation begins with stimulus (Any detectable input).
• Threshold: Dividing point between energy levels that do and do not have a detectable
o Absolute Threshold: Minimum amount of stimulation that an organism can
• As stimulus intensity increases, subjects’ probability of responding to stimuli
www.notesolution.com • Absolute threshold as the stimulus intensity detected 50% of the time.
Weighing the Differences: The JND
• Just Noticeable Difference (JND) –The smallest difference in the amount of
stimulation that a specific sense can detect.
• JND closely related to absolute threshold. Absolute Threshold is simply the JND
• Weber’s Law: States that the size of JND is a constant proportion of the size of the
initial stimulus. The constant proportion is called the Weber Fraction.
• Weber Fraction for weights: 1/30. This means you can only tell the difference
between 300 grams and 310 grams, not 300 grams and 305 grams.
• Scale – Judging the increase in sensory input.
• Fechner’s Law – The magnitude of a sensory experience is proportion to the number
of JNDs that the stimulus causing the experience is above the absolute threshold.
o Ex: Being in a darkroom, and turning on one light bulb. Second light bulb you
notice a small difference. Third one you hardly notice anything different.
• Perception can’t be measured on absolute scales.
• Signal-detection theory – The detection of stimuli involves decision processes as well
as sensory processes, which are both influenced by a variety of factors besides
• Hits – Detecting signals when present. Misses – Failing to detect signals when
present. False Alarms – Detecting signals when not present. Correct Rejections
– Not detecting signals when they are absent.
• Noise – Irrelevant stimuli that interferes with your ability to pick up weak signals.
Perception without Awareness
• Subliminal Perception – Registration of sensory input without conscious awareness.
(Limen = Threshold, sub = below. Therefore Subliminal = Below Threshold.
• Sensory Adaption – Gradual decline in sensitivity due to prolonged stimulation.
The Visual System
The Stimulus Light
www.notesolution.com • Light is a form of electromagnetic radiation that travels as a wave, moving at speed
• Amplitude affects perception of brightness, wavelength affects perception of colours.
• Purity influences perception of the saturation/richness of colours.
The Eye: A Living Optical Instrument
• Eye serves 2 main purposes: Channel light to the neural tissue (Retina), and housing
• Light enters the eye through the cornea. Than the cornea and the lens form and
upside down image of objects on the retina.
• Lens – transparent eye structure that focuses the light rays falling on the retina.
o Made up of soft tissue, that can make adjustments in itself in process called
accommodation. (Focusing on close object, lens = big. Focusing on far object,
lens flattens out.
• Nearsightedness – Close objects clear, but distant blurry. Eye is long.
• Farsightedness – Far objects clear, close blurry. Eye is short.
• Eye is always moving and scanning for information. These movements are called
The Retina: The Brain’s Envoy in the Eye.
• Retina is the neural tissue lining the inside back surface of the eye; it absorbs light,
processes images, and sends visual information to the brain.
• The axon that runs from retina to brain, converges at optic disk. Optic Disk – A hole
in the retina where the optic nerve fibres exit the eye. Since it is a hole, you can’t see
images which fall on it. This is called a blind spot. Your other eye compensates for
the blind spot.
Visual Receptors: Rods and Cones
• Only 10% of light arriving at cornea reach the receptors.
• Retina has two types of receptors: Rods and Cones.
• Rods outnumber cones. Average humans have 100m rods, but only 5m cones.
• Cones – Specialized visual receptors involved in daylight vision and colour vision.
Handle most daylight vision because bright light dazzles the rods. Provide Visual
Acuity (Sharpness and Preciseness)
• Fovea – Tiny spot in the centre of the retina that contains only cones.
• Rods – Specialized visual receptors involved in nightvision and peripheral vision.
• Averted Vision – Looking below or above object to look at it in darkness.
• Dark Adaption – Process in which eye becomes sensitive to light in low illumination.
(Stumbling around blindly, but within minutes your eyes adapt for example)
• Light Adaption – Process whereby the eyes become less sensitive to light in high
illumination. (Squinting when entering light area for example.
www.notesolution.com Information Processing in the Retina
• Receptive Field – Retinal area that, when stimulated, affects the firing of that cell to
• Lateral Antagonism (AKA Lateral Inhibition) – Occurs when neural activity in a cell
opposes activity in surrounding cells.
Vision and the Brain
• Visual Information gets to the brain from axons leaving the back of the eye form the
optic nerves which travel to the optic chiasm. After reaching optic chiasm, optic
nerve fibres diverge into two paths.
o Main pathway goes to Thalamus and synapse in the lateral geniculate
nucleus (LGN). The LGN processes visual signals and then sends to occipital
lobe that makes up the primary visual cortex.
When they synapse, it splits into two more pathways (Magnocellular
and Parvocellular channels)
These channels engage in parallel processing (simultaneously
extracting different kinds of info from the same input)
Parvo handles perception of colour, while magno handles brightness.
o The second pathway goes to superior colliculus in the midbrain and then into
the thalamus and onto the occipital lobe. The second pathway controls
• Optic Chiasm – Point at which the optic nerves from the inside half of each eye cross
over and then project to the opposite half of the brain.
Information Processing in the Visual Cortex
• Feature Detectors – Neurons that respond selectively to very specific ffeaturees
of more complex stimuli.
• After visual input processed in primary visual cortex, it is often routed to other
cortical areas for additional processed. These signals travel through two streams:
o Ventral Stream: Processes what objects are there (perception of form and
o Dorsal Stream: Where objects are (Perception of motion and depth)
Multiple Methods in Vision Research
• McCollough Effect
o Afterimage phenomenon.
• Visual Agnosia – Inability to recognize familiar objects.
www.notesolution.com Viewing the World in Colour
The Stimulus for Colour
• People can discriminate amongst 1 million colours.
• Two kinds of colour mixture:
o Subtractive Colour Mixing: Removing wavelengths of light, leaving
less light than was originally there.
o Additive Colour Mixing: Superimposing lights, putting more light
in the mixture than exists in any one light by itself.
• Trichromatic Theory of Colour Vision
o Also known as the Young-Helmholtz theory
o Theory states that the human eye has three types of receptors
associated with different wavelengths.
o These three receptors are for blue (short), green (medium), and red
o Colour-blindness: Dichromatic vision only. Only see 2/3 colours.
• Opponent Process Theory of Colour Vision
o Trichromatic was able to explain some things, but not others like
o Complementary Colours: Pairs of colours that produce grey tones
when mixed together.
o Afterimage – a visual image that persists after an image is removed
(for example: Looking at a strong colour than at a white wall)
o The colour of the after image is the complementary colour of the one
you looked at.
o People cannot explain many colours only using red, blue, and green.
They often need a fourth, yellow.
o The opponent process theory says that colour perception depends on
receptors that make antagonistic responses to three pairs of colours.