PSYA01H3 Chapter Notes - Chapter 4: Nociceptor, Nociception, Sound Localization
Chapter 4: Sensation and Perception
4.1 Sensation and Perception at a Glance
• Absolute threshold – the minimum amount of energy or quantity of a stimulus required
for it to be reliably detected at least 50% of the time it is presented
• Bottom-up processing – perceive individual bits of sensory information and use them to
create a more complex message
• Difference threshold – the smallest difference between stimuli that can be reliably
detected at least 50% of the time
o When you detect a difference, it is a just noticeable difference
o Depends on the intensity of the previous stimulus
o More intense the previous, the larger amount needed to reach the difference
threshold
• Divided attention – paying attention to more than one task at the same time
• Doctrine of specific nerve energies – different senses are separated in the brain
• Inattentional blindness – a failure to notice clearly visible events or objects because
attention is directed elsewhere n
• Perception – involves attending to, organizing, and interpreting stimuli that we sense
• Psychophysics – the field of study that explores how physical energy such as light and
sound and their intensity relate to psychological experience
• Selective attention – involves focusing on one particular event or task
• Sensation – the process of detecting external events with sense organs and turning
those stimuli into neural signals
• Sensory adaptation – the reduction of activity in sensory receptors with repeated
exposure to a stimulus
• Signal detection theory – states that whether a stimulus is perceived depends on both
the sensory experience and the judgement made by the subject
o Sensory process of presenting faint stimulus or no stimulus
o Decision process – was stimulus there?
o Hit, correct rejection, false alarm, miss
• Top-down processing – our perceptions are influenced by our expectations or by our
previous knowledge
• Transduction – specialized receptors transform the physical energy of the outside world
into neural impulses
• Weber’s law – the just noticeable difference between two stimuli changes as a
proportion of those stimuli
• Detecting then translating world into what we understand happens in 2 steps: sensing
and perceiving
• We have an internal representation of the world
• Stimulus -> sensory receptors -> neural impulses -> perception
• Orienting response – how we quickly shift our attention to stimuli that signal a change in
our sensory world
• Gustav Fechner (1801-1887) – German physicist interested in vision
o Helped create psychophysics
o Stimulus necessary for detection
• Ernest Weber (1795-1878) – a German physician and one of the founders of
psychophysics
• Subliminal perception – perception below the threshold of conscious awareness
• Priming – previous exposure to a stimulus influences later response to same stimulus or
related stimulus
o Subliminal priming can activate existing state, not create a new state
• Gestalt psychology – the whole is greater than the sum of its parts
o Figure-ground principle – objects stand out against a background
o Proximity – group together items
o Similarity – see similar things rather than contrast
o Continuity – view items as whole figures even if image is broken into many
segments
o Closure – fill in gaps to see a whole object
• Phonetic reversal – a word pronounced backwards sounds like another word
• Perceptual set – a filter that influences what aspects of a scene we perceive or pay
attention to
4.2 The Visual System
• Binocular depth cues – distance cues that are based on the differing perspectives of
both eyes
• Cones – photoreceptors that are sensitive to the different wavelengths of light that we
perceive as colour
o Clustered around the fovea
• Convergence – occurs when the eye muscles contract so that both eyes focus on a single
object
• Cornea – the clear layer that covers the front portion of the eye and also contributes to
the eye’s ability to focus
• Dark adaptation – the process by which the rods and cones become increasingly
sensitive to light under low levels of illumination
• Fovea – the central region of the retina
• Iris – round muscle that adjusts the size of the pupil
o Gives color to eyes
• Lens – a clear structure that focuses light onto the back of the eye
o Accommodation – lens can change its shape to focus light on the back of the eye
• Monocular cues – depth cues that we can perceive with only one eye
