Sensation and Perception

True or False? Advertisers are able to shape our buying habits through subliminal messages. If we stare at a green square for a while and then look at a white sheet of paper, we see red. Touching adjacent cold and pressure spots triggers a sense of wetness. People who are born without the ability to feel pain may die by early adulthood. Without their smells, a cold cup of coffee may be hard to distinguish from a glass of red wine. Infants just learning to crawl do not perceive depth Persons who have sight in only one eye are totally unable to gauge distances. A person who is born blind but gains sight as an adult cannot recognize common shapes and forms. If required to look through a pair of glasses that turns the world upside down, we soon adapt and coordinate our movements without difficulty. Laboratory evidence indicates that some people do have ESP.

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 Top-down 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 Ex. Whisper Difference threshold Minimum difference between two stimuli that can be detected 50% of the time Ex. Change in room temperature

Subliminal sensations Sensations not strong enough to be perceived May be processed sometimes May result in understanding without conscious awareness 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 Optic chiasm Thalamus Primary visual cortex 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

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

Perceptual organization How do we form meaningful perceptions from sensory information?

Gestalt psychology Branch of cognitive psychology Organization of many sensations into perceptions of wholes Based on experience and expectations Perceived whole is not always the same as its parts!

Form perception Simplification into easily interpretable wholes Figure-ground

Form perception Grouping principles Proximity Similarity Continuity Connectedness Closure

Depth perception Distance is perceived with vision and hearing Visual depth perception Binocular cues Monocular cues

Binocular depth cues Retinal disparity Strongest visual depth cue

Monocular depth cues Light and shadow Relative size and position Relative height/vertical position Linear perspective

Auditory location cues Intensity and pitch Arrival times at each ear Clarity

Perceptual constancy Cognitive functions that maintain the features of an object, despite changing illumination, color, size, or shape Based on comparisons between the figure and ground

Color and lightness constancy Consistent color and light intensity, despite changes in illumination

Shape and size constancy Familiar objects are perceived as unchanging despite changes in retinal images.

Perceptual interpretation Making sense of the perceptions produced by the cortex Genetics Experience Critical periods Plasticity and adaptation

Perceptual set Psychological predisposition to perceive stimuli in a particular way Shaped by learned assumptions and beliefs Affects how we interpret sensory stimuli Examples

Other sensory modalities

Hearing Stimulus - sound waves Frequency Amplitude

The ear

Auditory stimuli Bending of hair cells in the cochlea transduces vibrations into neural signals Auditory nerve Primary auditory cortex Auditory association cortex

Touch Stimulus - pressure, pain, warmth, cold Receptors Other sensations Stimuli organized in primary somatosensory cortex Perceptions created in somatosensory association cortex

Pain Critical alert system Subjective Physiology Prior experiences Attention Context Culture

Pain Gate-control theory Pain control/management

Taste Stimulus - chemical molecules that impart the sensations of sweet, sour, salty, bitter and umami Tastebuds contain taste and touch receptors

Taste perception Flavor Begins in brainstem Based on taste, olfactory, and touch stimuli Begins in brainstem Completed in the limbic system

Taste preferences Genetic predisposition Biological predisposition Learned responses

Smell Stimulus - chemical molecules Receptors in olfactory epithelium Axons project directly to the olfactory bulb of the brain Perception begins in the olfactory bulb, completed in the limbic system

Kinesthesis & vestibular sense Kinesthesis - sense of body position and movement Vestibular sense - sense of head postion and movement Stimulus - gravity and movement Receptors found in muscles (body) and inner ear (head)

Kinesthesis & vestibular sense Sensory signals about position and movement are organized in the medulla and cerebellum Perception occurs throughout the brain Brain stem Temporal cortex