March 10 2015 Chapter 3 Sensation and Perception Textbook Notes Introduction Synesthesia joined sensation or confusion of senses 2 4 of population may experience some form of synesthesia Causes are still being investigated but it appears some forms that signals that come from sensory organs such as the eyes or ears go to places in brain where they weren t originally meant to be and are processed differently Section 1 The ABCs of Sensation Sensation process by which info from the outside world enters the brain Sensation occurs when special receptors in the sense organs are activated allowing various forms of outside stimuli to become neural signals in the brain Related to the activation of receptors in the various sense organs Sense organs eyes ears nose skin and taste buds Related to changes in physical stimuli Detected by sensory receptors specialized forms of neurons the cells that make up the nervous system Sometimes ignored through sensory adaptation or cognitive habituation Transduction process of converting outside stimuli such as light into neural activity Instead of receiving neurotransmitters from other cells the sensory receptor cells are stimulated by different kinds of energy Examples Receptors in eyes are stimulated by light Receptors in ears are activated by vibrations Receptors for touch are stimulated by pressure or temperature Receptors for taste and smell are triggered by chemical substances Each receptor type transduces the physical info into electrical info in different ways which either depolarizes or hyperpolarizes the cell causing it to fire more or to fire less based on the timing and intensity of info it is detecting from the environment Sensory Thresholds Ernst Weber created Weber s law of just noticeable difference jnd or the difference threshold jnd is the smallest difference between two stimuli that is detectable 50 of the time whatever the difference between stimuli might be it is always a constant For example to notice diff in amount of sugar a person would need to add to a cup of coffee that is already sweetened with 5 teaspoons is 1 teaspoon then the of change needed to detect jnd is 1 5th or 20 If the coffee has 10 teaspoons of sugar in it the person would have to add another 20 or 2 teaspoons to be able to taste the diff half of the time Weber s Law example conclusion more people notice difference in the darker circles The more intense the stimulus light circle in the study the harder it is to detect differences March 10 2015 Absolute threshold Gustav Fechner expanded on Weber s theory the lowest level of stimulation that a person can consciously detect 50 of the time the stimulation is present Subliminal stimuli stimuli that are below the level of conscious awareness 1970s topic stimulation that we can t consciously detect The reality is it usually doesn t change behavior Just strong enough to activate the sensory receptors but not strong enough for people to be consciously aware of them Limin threshold Sublimin below the threshold Subliminal perception process by which subliminal stimuli act upon the unconscious mind influencing behavior 1957 James Vicary claimed showing advertising message for popcorn and Coca Cola while they watched a film prompted them to buy more of these two things After 5 years Vicary admitted he never conducted a real study Furthermore many researchers have gathered scientific evidence that subliminal perception doesn t work in advertising Stimuli can influence automatic reactions such as an increase in facial tension rather than direct voluntary behaviors such as going to buy something suggested by advertising Can influence brief emotions or feelings not long term behaviors Habitation and Sensory Adaptation Habituation the tendency of the brain to stop attending to constant unchanging info from the environment Lower centers of brain filter sensory stimulation and ignore or prevent conscious attention to stimuli that doesn t change Example people don t hear the noise that air conditioner makes unless it is suddenly cut off although they are actually hearing it they aren t paying attention to it Sensory adaptation the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging or constant All of our senses are subject to sensory adaptation Example what makes you get use to glasses bras underwear piercings etc In habituation the sensory receptors are still responding to stimulation but the lower centers of brain are not sending the signals from those receptors to the cortex The process of sensory adaptation differs bc the receptor cells themselves become less responsive to unchanging stimulus and receptors no longer send signals to the brain Microsaccades saccadic movements constant movement of eyes tiny little vibrations that ppl don t notice consciously Prevent sensory adaptation to visual stimulus Eyes are never entirely still Keep eyes from adapting to what they see Good thing bc otherwise you would go blind from staring off into space or focusing on one thing 3 1 How does sensation travel through the central nervous system and why are some sensations ignored Sensation is the activation of receptors located in the eyes ears skin and nasal cavities and tongue March 10 2015 Sensory receptors are specialized forms of neurons that are activated by diff stimuli such as light and sound Section 2 The Science of Seeing Light Albert Einstein proposed light is actually tiny wave packets called photons and have specific wavelengths associated with them Is a physical stimulus A form of electromagnetic radiation with properties of both waves and particles Processed by the eye Cornea Pupil Lens Retina final stop for light in the eye Light sensitive area Responsible for absorbing and processing light info Contains three layers ganglion cells bipolar cells and photoreceptors that respond to various wavelengths of light o Contains photoreceptors cells special receptor cells begins with retinal receptor cells Rods and cones sight visual sensory receptors found at the back of the retina are the business end of the retina the part that actually receives the photons of light and turns them into neural signals for the brain sending them first to the bipolar cells a type of interneuron called bipolar or two ended bc they have a single dendrite at one end and a single axon on the other and then to the retinal ganglion cells whose axons form the optic nerve 20 rods to one cone Lecture said 4 to 1 Rods