Chapter 9: Sense and Perception Flashcards
What is blindsight?
patient can’t identify objects in blind area
but can accurately tell about changes in visual field
patient not conscious that they can register changes in visual field
What is the relationship between blindsight and perception?
NS must construct images from bits of information
the brain must bind it all together, whole image perception
selective awareness: we can only access some part of the information our brain is currently processing
What is the nature of sensation and perception?
the only input our brain receives from the “real” world is a series of action potentials originating from external energy that are transduced by our sensory receptors
this info is passed along sensory neurons that form specific pathways
how we end up perceiving one set of nerve impulses as vision and another set as hearing is unknown
How are sensory system diverse?
vision, touch, taste, etc.
lead to different perceptual experience
but each sensory system is organized similarly
What are sensory receptors?
specialized cells that transduce (convert) sensory energy into neural activity
each sensory system’s receptors are designed to respond only to a narrow band of energy
vision: light energy produces chemical energy
auditory: air pressure produces mechanical energy
somatosensory: mechanical energy
taste and olfaction: chemical molecules
What is the receptive field?
region of sensory space (e.g. skin surface) in which a stimulus modifies a receptor’s activity
what the open eye sees is the receptive field of that eye
each photoreceptor in the eye points in a slightly different direction, so each one has a unique receptive field
RF helps us sample sensory information and can locate events in space
What is the relationship between sensory receptors and the receptive field?
sensory receptor receptive field can contrast the information each receptor is providing
adjacent receptive field may overlap
the contrast between their responses to events help us localize sensations
this spatial dimension of sensory information produces cortical patterns and maps that form each person’s sensory reality
What is receptor density and sensitivity?
sensory receptors are not evenly distributed across the body or its organs
density is important for determining the sensitivity of a sensory system, visual receptors packed towards the center of our visual field, peripheral vision is poorer
differences in receptor density determine the special abilities of many animals
What are neural relays?
all receptors connect to the cortex through a sequence of intervening neurons
sensory information is modified at each stage in the relay, each region constructs different aspects of the sensory experience
neural relays allow sensory systems to interact
What is sensory coding?
after transduction, sensory information is encoded by action potentials that travel along peripheral nerves to the CNS
from there, action potential travel on nerve tracks within the CNS, each bundle carries the same kind of signal
presence of a stimulus can be encoded by an increase or a decrease in discharge rate (the amount of increase/decreases can encode stimulus intensity)
changes in the visual field can be encoded by activity in different neurons or different levels of discharge within a neuron
What is representation of sensory coding?
the neocortex represents the sensory field of each sensory modality as a spatially organized neural representation of the external world
topographic map is a spatially organized neural representation of the external world
in mammals, each sensory system has at least one primary cortical area
these may project to secondary areas
What is the topographic map in the sensorimotor cortex?
the size of its features represent the relative proportions of the parts of the human brain responsible for motor and somatosensory function
the features that are most exaggerated have the largest correlate representations in the brain
What is sensation?
registration of physical stimuli from the environment by the sensory organs
sensory impressions are influenced by context, emotions, and memory
What is perception?
subjective interpretation of sensations by the brain
our visual experience is not an objective reproduction of what is out there, rather it is a subjective construction of reality that is manufactured by the brain
What is the cornea?
clear outer covering
controls and focuses the entry of light into the eye
What is the iris?
opens and closes to allow in more or less light
the hole in the iris is the pupil
What is the lens?
focuses light
bends to accommodate near and far objects
What is the retina?
where light energy initiates neural activity
light-sensitive surface at the back of the eye, consists of neurons and photoreceptor cells
translates light into action potentials
discriminates wavelengths (colors)
works in a wide range of light intensities
What is the fovea?
region at the center of the retina that is specialized for high acuity
receptive field at the center of the eye’s visual field
What is the acuity across the visual field?
vision is better in the center of the visual field than at the margins, or periphery
letters at the periphery must be much larger than those in the center for us to see them as well
What is the blind spot?
region of the retina where axons forming the optic nerve leave the eye and where blood vessels enter and leave
has no photoreceptors
visual fields overlap: left eye can see the right eye’s blind spot, brain compensation
What are photoreceptors?
the retina’s photoreceptor cells convert light energy first into chemical energy and then into neural activity
light arriving at photoreceptor triggers a series of chemical reactions
leads to a change in membrane potential
leads to a change in the release of neurotransmitters onto nearby neurons
What are rods?
more numerous than cones
sensitive to low levels of light (dim light)
used mainly for night vision
one type of pigment only
What are cones?
highly responsive to bright light
specialized for color and high visual acuity
in the fovea only
three types of pigment
What are the three types of cone pigments?
absorb light over a range of frequencies
blue, or short wavelength
green, or middle wavelength
red, or long wavelength
there are approximately equal numbers of red and green cones, but fewer blue cones
What are the types of retinal neurons?
bipolar cell: receives input from photoreceptors into ganglion cells
horizontal cell: links photoreceptors and bipolar cells
amacrine cell: links bipolar cells and ganglion cells
retinal ganglion cell (RGC): gives rise to the optic nerve
What are the two types of ganglion cells?
magnocellular cell (M-cell)
parvocellular cell (P-cell)
What are magnocellular cells?
magno-, large
receives input primarily from rods
sensitive to light and moving stimuli
What are parvocellular cells?
parvo-, small
receives input primarily from cones
sensitive to color
What is the optic chiasm?
junction of the optic nerves from each eye
axons from the nasal (inside) half of each retina cross over to the opposite side of the brain
axons from the temporal (outer) half of each retina remain on the same side of the brain
information from the left visual field goes to the right side of the brain, information from the right visual field goes to the left side of the brain
What are the three routes to the visual brain?
two main pathways lead to the visual cortex in the occipital lobe
geniculostriate pathway for processing the object’s image (made by all P ganglion axons and some M ganglion axons)
tectopulvinar pathway for directing rapid eye movements (made by remaining M ganglion axons)
another smaller pathway tracks into the hypothalamus
What is the geniculostriate system?
projections from the retina to the lateral geniculate nucleus to layer IV of the primary visual cortex
bridges the thalamus (geniculate) and the striate cortex)
