Chapter 5: The Perceiving Mind- Sensation and PerceptionHow does Sensation Lead to Perception?- Sensation- the process of detecting environmental stimuli or stimuli arising from thebody- Sensory systems have developed through natural selection- Perception- the process of interpreting sensory informationSensory Information Travels to the Brain- Sensation begins with interaction between a physical stimulus and our biological sensory systems.- Stimulus- anything that can elicit a reaction from our sensory systems- Transduction- the translation of incoming sensory information into neural signalsThe Brain Constructs Perceptions from Sensory Information- Attention- a narrow focus of consciousnesso Often determines which features of the environment influence our subsequent thoughts and behaviors- Unfamiliar, changing, or high- intensity stimuli impact our survival and have high priority for our attention- Sensory adaptation- the tendency to pay less attention to a non-changing source of stimulation- To prioritize input, we use selective attention, or the ability to focus on a subset of available information and exclude the rest- Bottom-up processing- perception based on building simple input into more complex perceptionso Simple thingso Only need this to respond appropriately to simple stimuli- Top-down processing- a perceptual process in which memory and other cognitive processes are required for interpreting incoming sensory informationo Reading a sentenceo Recognizing a friend in a crowdMeasuring Perception- Psychophysics- The study of relationships between the physical qualities of stimuli and the subjective responses they produceo Allows us to establish the limits of awareness, or thresholds, for each of our sensory systemso Developed by Gustav Fechner- Absolute threshold- the smallest amount of stimulus that can be detected- Difference threshold- the smallest detectable difference between two stimulio As stimuli get larger, differences must also become larger to be detectedSignal Detection- Signal detection- the analysis of sensory and decision making processes in the detection of faint, uncertain stimulio Two step process 1) the actual intensity of the stimulus, which will influence the observer’s belief that the stimulus did occur 2) the individual observer’s criteria for deciding whether the stimulus occurredHow Do We See?- Vision- the sense that allows us to process reflected light- 50% of our cerebral cortex processes visual informationVisual Stimulus- visible light is a type of radiation emitted by the sun, other stars, and artificial sources such as the lightbulb- energy moves in waves- Wavelength is decoded by our visual system as color or shaes of grey- The height of the waves is translated by the visual system into brightnessThe Biology of Vision- The eyeo Hard outer covering helps the fluid-filled ball retain shapeo Cornea- the clear surface at the front of the eye that begins the process of directing light to the retinao Pupil- an opening formed by the iriso Iris- the brightly colored circular muscle surrounding the pupil of the eye Adjusts the opening of the pupil in response to the amount of light present and to signals from the autonomic nervous system Arousal- dilated pupils Relaxation- constricted pupilso Lens- the clear structure behind the pupil that bends light toward the retina Muscles attathed to the lens can change its shape, allowing us to adjust our focus to see near or distant objectso Retina- layers of visual processing cells in the back of the eye A thin but complex network of neurons specialized for the processing of light In the deepest layer of the retina are specialized receptors called rods and cones that transduce the light info Before light reaches these receptors, it must pass through numberous blood vessels and neural layers We do not see the vessels and neural layers due to adaptation  Sensory systems tune out stimuli that never changeo Optic disk- where blood vessels leave the retina to form the optic nerve exit Because there are no rods or cones in here, the eye has a blind spoto Fovea- an area of the retina that is specialized for highly detailed vision Responsible for central vision as opposed to peripheral visiono The image projected on the retina is upside down and reversed relaive to the actual orientation fo the object being viewedRods and Cones- Rod- a photoreceptor specialized to detect dim lighto More sensitive to lighto More common as you move from the fovea to the periphery of retinao Do not provide info about coloro Not clear, sharp images- Cone- a photoreceptor in the retina that processes coloro Excel at seeing dim lighto Function best under bright lighto See sharp images and color- Human eye contains about 120 million rods and 6 million conesVisual Pathways- Rods and cones are the only true receptors of the visual system- They trigger responses in four additional layers of neurons within retina- Optic nerve- the nerve exiting the retina of the eye- Chiasm- the point at which the optic nerves cross the midline- Optic tracts- nerve pathways traveling from the optic chiasm to the thalamus, hypothalamus, and midbrain- The thalamus sends info about vision to the amygdala and primary visual cortex in occipital lobe- Primary visual cortex responds to shape, location, movement, and color- Parietal pathway- process movement in the visual environment- Temporal pathway- responds to shape and color and contributes to our ability to recognize objects and facesVisual Perception and CognitionColor Vision- Red green and blue are primary colors- Trichromacy theory- a theory of color vision based on the existence of different types of cones for the detection of short, medium, and long wavelengtho One or no cones- see just black, white and greyo Two cones- are color blindo Three cones- normal- Opponent process theory- a theory of color vision that suggests we have a red-green color channel and a blue-yellow color channel in which activation of one color in each air inhibits the othero We cannot see a color like “reddish-green” or “bluish-yellow” because they share the same channelRecognizing Objects- Feature detector- a hypothetical cell that responds to only one specific visual stimulus- The visual system may perform a mathematical analysis of the visual field- While the hierarchical model implies a reality built out of indivudial bars and edges, the mathematical approach suggest that we