Sensation and perception Fatmah Sakran 200901078

Definitions Sensation: The detection of physical energy emitted or reflected by physical objects Occurs when energy in the external environment or the body stimulates receptors in the sense organs. perception: The process by which the brain organizes and interprets sensory information.

Stimulation Becomes Perception

Principles of sensation Transduction - Physical energy to neural signal Sensory receptors – Specialized neurons that are activated by stimulation and transduce (convert) the incoming stimulus into electrochemical signals

Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain Sensory Adaption - refers to the fact that repeated or constant stimulation decreases the number of sensory messages sent to the brain, which causes decreased sensation.

Thresholds Absolute threshold:- smallest strength of a stimulus tat can be detected Difference threshold :- (jnd) smallest difference that can be detected

Thresholds Weber’s law – The size of the JND is proportional to the intensity of the stimulus The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low

Determining which stimuli will actually become sensation . what the quality and impact of that sensation will be . and whether it grabs our interest

Comparison with personal standard Signal Detection Theory Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes Stimulus event Neural activity Comparison with personal standard Action (or no action)

How Are the Senses Alike? How Are They Different? - The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain

vision purpose of the visual system Transform light energy into an electrochemical neural response Represent characteristics of objects in our environment such as size, color, shape, and location.

Anatomy of Visual Sensation

Distribution of Rods and Cones Consentrated in peiphery Approx. 120 million Cones :- concentrated in center of eye (fovea). approx. 6 million Blind spot:- Point where the optic nerve exits the eye and where there are no photoreceptors. region with no rods or cones

Differences Between Rods and Cones Allow us to see in bright light Allow us to see fine spatial detail Allow us to see different colors Rods Allow us to see in dim light Can not see fine spatial detail Can not see different colors

Rods Cones

Retinal Photoreceptors Light passes through the retinal layers to reach the photoreceptors at the inner retinal surface. Photoreceptors and bipolar cells conduct potentials to the ganglion cells, which in turn initiate action potentials which are transmitted to the thalamus.

How the Visual System Creates Color and Brightness Wavelength Intensity (amplitude) Color Brightness

How the Visual System Creates Color Electromagnetic spectrum – -Entire range of electromagnetic energy, ---includes radio waves, X-rays, microwaves, and visible light Visible spectrum – -Tiny part of the electromagnetic spectrum that is visible to our eyes (INSERT IMAGE OF SPECTRUM HERE)

How the Visual System Creates Color Trichromatic theory- Based on 3 cone receptors Explains initial stages of color vision Opponent-process theory– Based on bipolar cells Colors in complementary pairs Explains afterimages

Afterimages Afterimages – Sensations that linger after the stimulus is removed In the following slide, fix your eyes on the dot in the center of the flag

Complementary Afterimages

How the Visual System Creates Color Color blindness – Vision disorder that prevents an individual from discriminating certain colors

Vision Test of Color Deficiency

The Sound Stimulus

Hearing: If a Tree Falls in the Forest... The Physics of Sound Frequency – Number of cycles completed by a wave in a given amount of time Low Frequency High Frequency

Hearing: If a Tree Falls in the Forest... The Physics of Sound Amplitude – Physical strength of a wave High Amplitude Low Amplitude

Decibel levels of different sounds

Hearing The Human Ear Audition The sense of hearing

How We Hear Sound Waves Cochlea

Psychological Qualities of Sounds Pitch – Sensory characteristic of sound produced by the frequency of the sound wave Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave Timbre – Quality of a sound wave that derives from the wave’s complexity

Position and Movement Vestibular sense – Sense of body orientation with respect to gravity Receptors in semicircular canals Kinesthetic sense – Sense of body position and movement of body parts relative to each other Receptors in joints, muscles, and tendons

Smell Olfaction – Sense of smell Olfactory bulbs – Brain sites of olfactory processing Pheromones – Chemical signals released by organisms to communicate with other members of the species

Other Senses Olfactory System Structures responsible for the sense of smell

Other Senses Taste Buds Nets of taste-receptor cells This is a photograph of tongue surface (top), magnified 75 times. 10,000 taste buds line the tongue and mouth. Children have more taste buds than adults do. There are four primary tastes: sweet, salty, sour, and bitter.

Taste

The Skin Senses Protects against surface injury, holds in bodily fluid, and helps regulate body temperature Touch Warmth Cold Pain

Other Senses The Thermal Grill Temperature When a person grasps two braided water pipes – one with cold water running through it and one with warm water – the sensation is “burning hot” and painful. There are two separate pathways for warmth and cold.

Other Senses Pain Gate-control Theory Psychological control Theory that the spinal cord contains a neurological “gate”that blocks pain signals for the brain when flooded by competing signals. Psychological control Mind over sensation, distraction

Other Senses Coordination Kinesthetic System Vestibular System Structures distributed throughout body that sense position and movement of body parts. Vestibular System The inner ear and brain structures that afford a sense of equilibrium.

Keeping the Signals Straight Synesthesia Rare condition in which stimulation in one sensory modality triggers sensations in another sensory modality. Each sensory system designed to operate separately from the others. Selective Adaptation A decline in sensitivity to a stimulus as a result of constant exposure.

What is the Relationship Between Perception and Sensation? Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it

Perception Perceptual Organization Perceptual Constancies Depth and Dimension Perceptual Set The World of Illusions

Perceptual Organization Reversible Figures Drawings that one can perceive in different ways by reversing figure and ground. Gestalt Psychology School of thought rooted in the idea that the whole is different from the sum of its parts.

Perceptual Organization Gestalt Laws of Grouping Proximity Seeing 3 pair of lines in A Similarity Seeing columns of orange and red dots in B Continuity Seeing lines that connect 1 to 2 and 3 to 4 in C Closure Seeing a horse in D

Perceptual Organization Identifying Objects Geons (geometric icons) are simple 3D component shapes. A limited number are stored in memory. Geons are combined to identify essential contours of objects.

Perceptual Constancies Size Constancy The tendency to view an object as constant in size despite changes in the size of the retinal image. Shape Constancy The tendency to see an object as keeping its form despite changes in orientation.

Perceptual Constancies The Ames Room A specially-built room that makes people seem to change size as they move around in it The room is not a rectangle, as viewers assume it is. A single peephole prevents using binocular depth cues.

Perceptual Constancies Shape Constancy Even though these images cast shadows of different shapes, they still are seen as round.

Depth and Dimension Depth Perception Convergence Binocular Disparity The use of visual cues to estimate depth and distance. Convergence A binocular cue involving the turning inward of the eyes as an object gets closer. Binocular Disparity A binocular cue whereby the closer an object is, the more different the image is in each retina.

Depth and Dimension Monocular Depth Cues Distance cues that enable the perception of depth with one eye. Relative Image Size Texture Gradient Linear Perspective Interposition Atmospheric Perspective Relative Elevation Familiarity

Depth and Dimension The Visual Cliff Devised by Eleanor Gibson and Richard Walk to test depth perception in infants and animals. Provides visual illusion of a cliff. Caregiver stands across the gap. Babies are not afraid until about the age they can crawl.

Perceptual Set What is seen in the center figures depends on the order in which one looks at the figures: If scanned from the left, a man’s face is seen. If scanned from the right, a woman’s figure is seen.

Perceptual Set Context Effects The same physical stimulus can be interpreted differently depending on perceptual set, e.g., context effects. When is the middle character the letter B and when is it the number 13?

The World of Illusions The Müller-Lyer Illusion Illusion in which the perceived length of a line is altered by the position of other lines that enclose it

The World of Illusions The Ponzo Illusion Illusion in which the perceived line length is affected by linear perspective cues. Side lines seem to converge Top line seems farther away But the retinal images of the red lines are equal.

Extrasensory Perception The Case for ESP The Case against ESP The Continuing Controversy

The Case for ESP Extrasensory Perception (ESP) The ability to perceive something without ordinary sensory information. This has not been scientifically demonstrated. Parapsychologists distinguish between three types of ESP: Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events

The Case against ESP ESP Cards J. B. Rhine conducted many experiments on ESP using stimuli such as these. Rhine believed that his evidence supported the existence of ESP, but his findings were flawed..

The Continuing Controversy The ganzfield procedure Researchers disagree about the reliability of studies done to replicate the ganzfield test.

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