Sensation & Perception Flashcards
illusion absolute threshold (or absolute sensitivity) sensation just noticeable difference (jnd) perception Weber’s Law transduction signal detection theory sense receptor the McGurk effect sensory adaptation synesthesia psychophysics parallel processing bottom-up processing top-down processing perceptual set perceptual constancy selective attention inattentional blindness the binding problem
xTwo Interacting Aspects of Perception • Bottom-up processing – Processing based on incoming stimuli from the environment – Also called data-based processing • Top-down processing – Processing based on the perceiver’s previous knowledge (cognitive factors) – Also called knowledge-based processing
The Visual System trichromatic theory colour blindness opponent process theory depth perception monocular depth cues binocular depth cues binocular disparity (or retinal disparity) binocular convergence The Auditory System audition pitch / frequency / Hertz loudness / amplitude / Decibels timbre outer ear middle ear ossicles (or small bones) inner ear cochlea organ of Corti basilar membrane place theory frequency theory (including volley theory)
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What is perception?
a largely unconscious, automatic process, based on ‘unavailable’ neural events, together with ‘unconscious’ inferences from specific cues • but, at times conscious effort is needed to interpret sensory data (e.g., when data are ambiguous and incomplete) • effortlessness of perception disguises the complex nervous system mechanisms operating (behind the scenes)
Approaches to the Study of Perception
• Observing perceptual processes at different stages in the system: >Psychophysical approach (PP) - the stimulus-perception relationship >Physiological approach (PH1) - the stimulus-physiology relationship >Physiological approach (PH2) - the physiology and perception relationship • These stages are interconnected and communicate with one another.
Psychophysics - Overview of Methods of Measurement
Qualitative Methods
– Describing
– Recognising
Quantitative Methods
– Detecting
– Perceiving Magnitude
– Searching
Qualitative Methods of Psychophysical Measurement
Description
– Indicating characteristics of a stimulus
– First step in studying perception
– Called phenomenological method
Recognition
– Placing a stimulus in a category by identifying it
– Categorisation of stimuli
– Used to test patients with brain damage
Quantitative Methods - Classical Psychophysics
Absolute threshold
- smallest amount of energy needed to detect a stimulus – Method of constant stimuli
Five to nine stimuli of different intensities are presented in random order
Multiple trials are presented
Threshold is the intensity that results in detection in 50% of trials
Human eye
Retinal Processing -
Rods and Cones • Differences between rods and cones – Shape >Rods - large and cylindrical >Cones - small and tapered – Distribution on retina >Fovea consists solely of cones. >Peripheral retina has both rods and cones. >More rods than cones in periphery.
Convergence in the Retina •
126 million rods and cones converge to 1 million ganglion cells. – The ganglion cells therefore have ‘receptive fields’ resulting from information passed from a number of separate rods/cones. • Higher convergence of rods than cones – Average of 120 rods to one ganglion cell – Average of six cones to one ganglion cell – Cones in fovea have one to one relation to ganglion cells
Convergence and Sensitivity
Rods are more sensitive to light than cones. – Rods take less light to respond – Rods have greater convergence which results in summation of the inputs of many rods into ganglion cells increasing the likelihood of response. – Trade-off is that rods cannot distinguish detail
The Structuralist Approach
Approach established by Wundt (late 1800s) – States that perceptions are created by combining elements called sensations
The Gestalt Approach
• The whole differs from the sum of its parts. – Perception is not just built up from sensations, but is a result of perceptual organization. • Principles of perceptual organization. – Pragnanz - every stimulus is seen as simply as possible – Similarity - similar things are grouped together
