Sensation and Perception

Sensation and Perception

• Transformation of stimulus energy into a meaningful understanding– Each sense converts energy into awareness

Sensation

• Detection and encoding of physical stimuli into neural signals– Occurs at sensory receptors– External stimuli correspond to sensory

modalities– Light waves: ___________– Sound waves : ___________– Pressure, warmth, cold, pain : ___________– Chemical messengers : _________&__________– Body position and movement : _________&_________

Perception

• Organization of sensory information into cognitive awareness environmental stimuli– Occurs in the cerebral cortex

Processing stimuli

• Bottom-up processing– Scientific explanation– Begins with receptors and works up to

integration• Top-down processing

– Understanding stimuli based on prior experience and expectations

– The brain will rapidly interpret stimuli based on their “most likely” explanation

Thresholds of sensation

• Absolute threshold– Minimum stimulation

needed to detect a stimulus 50% of the time

• Difference threshold– Minimum difference between two stimuli that

can be detected 50% of the time

Subliminal sensations

• Sensations not strong enough to be perceived– May be processed sometimes– May result in understanding without conscious

awareness• Blindsight

• Useful persuasion method?

Sensory adaptation

• Diminished sensitivity to a continuous stimulus– Allows for focus on relevant stimuli

Vision

• Stimulus: visible light– Wavelength– Intensity

Vision

• Receptive organ: the eye

Photoreceptors

• Rods• Cones

Visual pathway

• Optic nerve– Exits retina

• Optic chiasm• Thalamus• Primary visual

cortex

Processing visual stimuli

• Feature detectors in the primary visual cortex respond to specific features in parallel– Form– Movement– Depth– Color

• This information is passed to higher levels of cortical processing for integration

Perception of visual stimuli

• Perception occurs in visual association areas in the occipital, parietal and temporal lobes

Color vision

• Young-Helmholtz trichromatic theory– Red, green, blue color receptors in the retina– Stimulation of one or many results in color sensation

• Opponent-process theory– Colors are analyzed in terms of opponent colors

• Red vs. Green• Yellow vs. Blue• Black vs. White

– One color turns some cells “on” and other cells “off”

Psychology of visual perception

• Top-down processing means that what we see is influenced by biological, psychological and socio-cultural factors

Perceptions are the result of interpretations by an experienced brain!