Chapter 6 Flashcards
When the pupils are constricted, the image falling on each retina is ___________ and there is a greater ____________.
sharper; depth of focus
The process of adjusting the configuration of the lenses to bring images into focus on the retina is called:
accommodation.
When we direct our gaze at something ___________, the lens tends to assume its natural _____________ shape.
near; cylindrical
Convergence is greatest when inspecting things that are:
close
Binocular disparity tends to be greater for _________ objects.
closer
_____ and _____ cells play a role in lateral communication within the human retina.
Amacrine; horizontal
______________ vision predominates in good lighting and provides high-acuity colored perceptions of the world. In contrast, the more sensitive ______________ vision predominates in low lighting.
Photopic; scotopic
The ______ effect can be observed during the transition from photopic to scotopic vision.
Purkinje
_____ are a type of involuntary fixational eye movements.
Saccades
Rhodopsin is a(n) ____________________ that responds to light rather than to neurotransmitter molecules.
G-protein–coupled receptor
About ___ percent of the axons of retinal ganglion cells become part of the retina-geniculate-striate pathways.
90
All signals from the right visual field reach the left primary visual cortex, either ipsilaterally from the _______________ of the left eye or contralaterally from the ____________ of the right eye.
temporal hemiretina; nasal hemiretina
Although the _________ constitutes only a small part of the retina, a relatively large proportion of the primary visual cortex is dedicated to the analysis of its output.
fovea
The retina-geniculate-striate system is _____________. This means two stimuli presented to adjacent areas of the retina will excite adjacent neurons at all levels of the system.
retinotopic
_______________ neurons are particularly responsive to color, fine pattern details, and stationary or slowly moving objects; in contrast, ________________ neurons are particularly responsive to movement.
parvocellular; magnocellular
The perception of edges ultimately boils down to the perception of:
contrast
The ___________________ of a visual neuron is the area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron.
receptive field
On-center and off-center cells respond BEST to:
contrast
The main difference between simple cortical cells and lower layer IV neurons is that the borders between the “on” and “off” regions of the receptive fields of simple cortical cells are ____________ rather than ______________.
straight; circular
Unlike simple cortical cells, which are all _______________, many complex cortical cells are _____________.
monocular; binocular
According to the ____________ theory, there are three different kinds of color receptors, each with a different spectral sensitivity.
component
According to the ____________ theory, if an increase in the response of a particular visual neuron signals green, a decrease signals red.
opponent
Most primates are ______________, whereas most other mammals are _______________.
trichromats; dichromats
_________________ constancy refers to the fact that the perceived color of an object is not solely a function of the wavelengths reflected by it.
Color
According to the ___________ theory of color vision, the color of an object is determined by its reflectance.
retinex
_______________ refers to the ability of certain patients to respond to visual stimuli in their scotomas even though they have no conscious awareness of the stimuli.
Blindsight
Most areas of secondary visual cortex are located in two general regions: the _______________ cortex and the __________________ cortex.
prestriate; inferotemporal
According to one theory, the dorsal stream is involved in the perception of __________________ and the ventral stream is involved in the perception of ___________________.
where objects are; what objects are
__________________ is a visual agnosia for faces.
Prosopagnosia
_________________ is a deficiency in the ability to see movements progress in a normal, smooth fashion.
Akinetopsia
What type of physical energy is transduced into electrochemical signals by specialized sensory neurons in each of our five primary sensory systems?
Vision: photons
Audition: sound waves
Somatosensation: pressure, vibration, heat/ cold
Taste/ Smell:chemicals
What does each type of photoreceptor cell respond to, and how are the different types distributed in the retina?
Rods: low-light vision ( no detail or color)
Many rods → a few bipolar cells → ganglion cells
Cones: high light vision (detail and color)
Each cone → bipolar cells → ganglion cells
What happens when the photoreceptor cells (rods, cones) are exposed to light?
Rods and cones hyperpolarize, no longer stimulate bipolar cells
What are the 3 major layers of neurons that make up the retina, and what is the direction of communication to the brain? (i.e., how does light ultimately become an action potential?)
back front
Photoreceptor → Bipolar cells → Ganglion cells
First photoreceptors transduce light sends signals too bipolar cells, then they send signals to ganglion cells
What is the most common cause of color-blindness?
Due to genetics, the most common type of color blindness is red-green (8%)
Explain how visual information from right and left eyes compared to the right and left visual fields gets into the brain.
Everything from the left visual field goes to the right hemisphere even if it’s picked up by the right eye and vise versa
Describe the “major” and “minor” pathways of visual information processing from retinal ganglion cells to the brain.
Major: Retina → LGN → Primary visual cortex (occipital lobe) → secondary visual pathway –> assoc. (ventral/ dorsal)
Minor: Retina → Superior colliculus (midbrain tectum) → Post parietal lobe
Explain at least one mechanism by which our brains process visual information to sharpen our perception of edges (e.g., enhance our ability to visually distinguish objects from background).
Lateral inhibition: retinal and LGN: neurons firing maximally to the bright side of a given edge inhibit the firing of adjacent neurons- sharpening our edge perception
Center- surround firing: vision neurons [retina (some r. Ganglion cells), LGN, primary visual cortex] are excited or inhibited depending on where in their receptive field light hits: in an “on-center” or “off-center” manner fire most strongly to contrast edges
What types of simple stimuli do individual primary visual cortex (V1) neurons respond to?
Simple cells: simple lines
- Input from only one eye
- Rectangular receptive fields with “on/off” areas
- Fire maximally to straight edge of particular orientations
Complex Cells: lines but also movement
- Particular orientation and movement direction
- Input from either eye or both (binocularity → depth perception)
Explain the change in visual perception that may be caused by single-hemisphere vs. dual-hemisphere damage to primary visual cortex (V1), and explain why people with extensive, dual-hemisphere V1 damage may still show some visual guided behavior, albeit “unconsciously.”
One hemisphere: one visual field will be damaged
Both hemispheres: cortical blindness (total or partial blindness), may experience a blind spot due to intact superior colliculus.
Some messages might be still sent down the dorsal stream (where/ how) but they are unaware of it
Describe the specific types of disturbances of visual perception that are associated with damage to secondary visual cortex areas V4 and V5, compared to inferior temporal lobe (inferotemporal cortex) and posterior parietal lobe. What are the various visual agnosias called, specifically?
V4 Damage: loss of normal color vision “achromatopsia”
V5 Damage: motion blindness “akinetopsia”
Agnosias: Ventral Stream damage
Object agnosia: inability o recognize previously familiar objects
Prosopagnosia: inability to recognize faces
In situations where the level of illumination is high and sensitivity is not important, the visual system responds by:
constricting the pupils of the eyes.
Ciliary muscles adjust the:
lens shape.
Photopic vision is:
cone-mediated.
Visual signals from the left nasal hemiretina are projected directly to the:
lateral geniculate nuclei.
An interior designer explains that turquoise is an underappreciated color because it is calming during the day but brightens a dim room in the evening. The _____ effect helps explain this perception.
Purkinje
The transduction of light by rods reflects a(n) _____ in the release of the neurotransmitter _____.
decrease; glutamate
Because of the way that it is organized, the visual system is referred to as:
retinotopic
At least two parallel channels of communication flow through each lateral geniculate nucleus. One runs through the ______________ layers and a second runs through the _____________ layers.
parvocellular; magnocellular
The mechanism of contrast enhancement is:
lateral inhibition.
In comparison to simple cortical cells, complex cortical cells:
are more numerous.
The major advantage of the retinex theory over the classic component and opponent process theories of color vision is that the retinex theory:
can explain color constancy.
Many persons with scotomas:
are not consciously aware of their deficits.
Damage to the fusiform face area is often associated with:
prosopagnosia.
Persons with a visual agnosia:
see objects but can’t identify them.
The middle temporal (MT) area of human cortex appears to play an important role in the perception of:
motion
