Describe the two ways used to conceptualize light
Light can be thought of as a wave that travels through a medium. Or it can be thought of as a stream of photon.
Describe the difference between light that is reflected and light that is transmitted.
Reflected light occurs when a ray of light strikes a light colored surface and then bounces back towards its point of origin. Transmitted light occurs when light is neither reflected nor absorbed by a surface. An example is a transparent window; light passes through the surface and is transmitted to the other side.
What is the purpose of the cornea?
The cornea is a transparent surface on the exterior of the eye. It protects the eye from the outside world. Being transparent, it allows light to be transmitted through it and into the eye.
What is the purpose of the retina?
The retina is a light sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve.
How does accommodation take place in the eye?
Accommodation takes place in the lens of the eye. The lens changes its refractive power by changing its refractive power by changing its shape. This causes the eye to be able to focus on a given object, whether it is near or far.
Why are photoreceptors important in the process of seeing?
Photoreceptors are the cells that make up the back most layer of the retina. They are sensitive to light, and as soon as they sense it, they can cause neurons in the intermediate layers to fire action potentials. Photoreceptors are important in the process of seeing because they transduce the physical energy of light into neural energy that our brains can analyze.
What are rods?
Rods are specialized photoreceptors in the eye that are specialized for night vision.
What are cones?
Cones are specialized photoreceptors that are specialized for daylight vision, fine visual acuity and color.
What is hyperpolarization?
Hyperpolarization is an increase in membrane potential in where the inner membrane surface becomes more negative than the outer membrane surface. This process is one in a sequence of events that occur once light is sensed by the photoreceptors,
Why can't rods signal color differences?
Rods can't signal color differences because they only have one type of photopigment. Cones, on the other hand have three types of photopigments, which help them to differentiate between colors.
What is the difference between an "on" bipolar cell and an "off" bipolar cell?
An "on" bipolar cell is a a small cone cell that depolarizes in response to an increase in light intensity. An "off" bipolar cell is a small cone bipolar cell that depolarizes in response to a decrease in light intensity. These two cells have opposite reactions to light.
What is a receptive field?
A receptive field is a the region on the retina in which stimuli will activate a neuron. Receptive fields vary in size, shape, and complexity.
Why is center-surround organization of retinal ganglion cells so important?
It allows for sensitivity to contrast rather than absolute illumination levels. Ganglion cells are most sensitive to differences in the intensity of light in the differences in the intensity of light in the center and in the surround, and they are relatively unaffected by the average intensity of light. This is useful because the average intensity of light falling on the retina will be variable depending on the environment.
What is a filter and how is it important in vision?
A filter allows the passage of some frequencies and blocks others. The filter is important in vision because it allows the transformation of the raw image into a representation by the brain. The filter highlights certain important visual information while it eliminates other unimportant information. The center-surround receptive fields of retinal ganglion cells are filters.
What are P ganglion cells?
P ganglion cells have smaller receptive fields. They provide greater acuity as long as there is enough light for them to operate.
What are M ganglion cells?
M ganglion cells have large receptive fields. They are sensitive to visual stimuli under low lighting.
How does the pupil adapt to dark and light conditions?
The pupil has the ability to dilate and constrict, depending on the amount of light. Under well-lit conditions, the pupil tends to constrict to let less light into the eye. Under dark conditions, the pupil dilates to allow more light into the eye.
What is psychophysics?
Psychophysics is the science of defining quantitative relationships between physical and psychology events.
What is the just noticeable difference (JND)?
The JND is the smallest detectable difference between two stimuli, or the minimum change in a stiumuls that can be correctly judged as different form a reference stimulus. It is also know as the difference threshold.
What is the method of constant stimuli?
The method of constant stimuli involves the presentation of many stimuli, ranging from rarely to almost always perceivable. They are presented one at a time and participants respond to each presentation with a "yes/no".
What is the method of limits?
The method of limits involves presenting stimuli that vary incrementally in one dimension until the participant responds differently.
What is the method of adjustment?
The method of adjustment is the psychophysical method, which uses the method of limits idea, but the participant controls the change in stimulus.
What is Fechner's law?
Fechner's law P=k*log(S)
P= perceived magnitude
Equal increments of stimulus intensity provide smaller and smaller perceived magnitude increases.
Why is the JND important in psychophysics?
It is the minimum change in stimulus that can be correctly judged as different from a reference stimulus. It is important to psychophysics because it helps experimenters make conclusions about how we perceive things.
What is signal detection theory?
Signal detection theory is a theory that quantifies the response of an observer to the presentation of an observer to the presentation of a signal in the presence of a noise. The signal is the target stimulus and the noise is the interference that occurs, and is sometimes confused with the signal.
What is magnitude estimation?
Magnitude estimation is a psychophysical method in which the participant assigns values according to perceived magnitudes of stimuli.
What is visual acuity and how can it be measured?
Visual acuity is the smallest spatial detail that can be seen accurately. It can be measured by doing a visual acuity test, which requires looking at figures from a distance and identifying them.
What can we infer from the contrast sensitivity function?
The contrast sensitivity function describes our window of visibility. Any object whose spatial frequencies and contrast fall within the region specified by the contrast sensitivity function will be visible. Those objects outside the region are outside our window of visibility. We can infer from this function that sensitivity to contrast depends on the spatial frequency of the stimulus.
How do retinal ganglion cells respond to stripes?
Each ganglion cell responds to certain types of stripes or gratings. For instance, an "on" ganglion cell responds to gratings with spatial frequencies and phases that make the lightest part of the grating fall on the center of the cell and the darkest part of the grating fall on the surround. When the spatial frequency of the grating is too low, the ganglion cell responds weakly because part of the bar of the grating lands in the inhibitory surround, damping the cell's response. Similarly, when the grating's spatial frequency is too high, the ganglion cell responds weakly because both dark and bright stripes fall within the receptive field's center and surround, washing out the response. When the frequency is just right, the cell responds vigorously.
What is the role of the lateral geniculate nucleus?
The lateral geniculate nucleus is a nucleus in the midbrain that shares connections with both the retina and visual cortex.
What are the two types of layers of the LGN and how are they different from each other?
The two types of layers of the LGN are the magnocellular layers and the parvocellular layers. The M layears are the two bottom layers of the LGN, and contain neurons that are physically larger than those in the parvocellular layers. Neurons in these layers respond to large, fast-moving objects. The parvocellular layers are the top four layers of the LGN. They contain neurons that respond to details of stationary objects.
What is topographical mapping?
Topographical mapping is the orderly mapping of the world in the LGN and the visual cortex. Points of light that are near each other in the world will be processed by neurons that are near each other in the brain. This orderly representation provides us with a neural basis of knowing where things are in space.
What is cortical magnification?
The dramatic scaling of information from different parts of the visual field. Objects on or near the fovea are processed by neurons in a large part of the striate cortex, while objects imaged in the periphery are allocated a much smaller portion of the striate cortex.
What is orientation tuning?
Orientation tuning is the tendency of neurons in the striate cortex to respond optimally to certain orientations, and less to others.
How do striate cortex neurons function as filters?
Each striate cortex neuron responds to a particular location and is tuned to a particular spatial frequency, orientation, and phase. These narrow tuning functions mean that each striate cortex neuron functions as a filter for the portion of the image that excites the cell.
What is ocular dominance?
Ocular dominance is the property of the receptive fields of striate cortex neurons by which they respond more vigorously when a stimulus is presented in one eye than when it is presented in the other eye.
What is the difference between simple and complex cells?
Simple cells are cortical neurons with clearly defined excitatory and inhibitory regions, while complex cells are neurons whose receptive field responds to any properly oriented bar of light, regardless of whether it is light or dark.
What is the role of end stopping?
End stopping refers to a property of hypercomplex cortical neurons. They only respond to bars of light with corners and angles of a specific length.They play an important role in our ability to detect luminance boundaries and discontinuities.
What does a hypercolumn contain?
A hypercolumn contains at least two sets of columns, each covering every possible orientation, with one set preferring input from the left eye and one set preferring input form the right eye.
How can adaptation provide insights into the properties of cortical neurons?
Adaptation is the diminishing response of a sense organ to a sustained stimulus. It is helpful in learning about the properties of cortical neurons because, by exposing an observer to a particular stimuli for an extended period of time, the experimenter can make inferences about the visual system due to the observer's changing response. If two stimuli are processed by unrelated sets of neurons, then selectively adapting one set of neurons should have no effect on the other set.
What are spatial frequency channels?
Spatial frequency channels are pattern analyzers, implemented by ensembles of cortical neurons, with each set of neurons tuned to a limited range of spatial frequencies.
Why can't we apply a simple rule like "homogeneous areas belong to the same object" in order to find an object's contours?
Because humans sometimes perceive object contours even in areas of an image where there is no physical difference between the object and its background.
What is an illusory contour?
An illusory contour is one that is perceived even though they are not present in the physical stimulus.
What is the guiding philosophy behind Gestalt psychology?
They believe that people perceive objects as a whole not as the sum of its parts
What was the guiding philosophy behind structuralism?
Structuralists believed that perception of a complex scene was simply the sum of basic "atoms" of perception in the scene.
Why are the Gestalt grouping principles important?
They provide rules for how different elements in an image should be combined by the visual system.
What is figure-ground assignment?
The process of determining which areas of an image constitute a "figure" and which areas form the background.
How does meaning play a role in figure-ground assignment?
People are more likely to identify a familiar shape as the figure than as the ground. This indicates that high-level object recognition processes are at work during the preliminary processing stage.
What do non-accidental features tell us about a scene?
Certain arrangements of edges can be interpreted as providing important information about segmenting objects in a scene, providing we are seeing the edges from a non-accidental view-point.
What rules do our perceptual committees use to divide objects into parts?
One widely accepted proposal is that we use valleys, rather than bumps, in an object as clues to where to divide the object into parts, cutting the object by connecting pairs of valleys.
What is the global superiority effect?
Provides evidence that the visual system starts with large objects and then divides them into smaller parts. It was easier for people to identify the large (global) letter than the the small (local) letters that created the large letter.
What is the fundamental goal of object recognition?
To match representation of perceived visual stimulus to a representation of a previously-encounter object encoded in memory.
What is a geon?
Geons are "geometric ions", the fundamental components of objects. They make the object easily recognizable from any viewpoint
What is viewpoint invariance?
Occurs when you can accurately perceive an object regardless of the viewpoint. However, people are usually slower at recognizing an object from a novel viewpoint.
What is the problem of univariance?
The problem of univariance is the fact that an infinite set of different wavelength intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make accurate color discriminations based on wavelength.
What are the three types of cones in the visual system?
S-cones, M-cones, and L-cones. They are all collectively responsible for discriminating between different colors. The S-cones are sensitive to short wavelengths, the m-cones are sensitive to middle wavelengths, and the L-cones are sensitive to long wavelengths.
What is the trichromatic theory of color vision?
The trichromatic theory of color vision tells us that the color of any light is defined in our visual system by the relationships between the outputs of the three cone types.
Why do metamers produce the same perceived color?
Metamers are different mixtures of wavelengths that look identical. Even though the wavelength mixtures are different, they produce the same response from the cones in our visual system, which in turn causes the colors to appear identical.
What is an additive color mixture?
An additive color mixture is when tow sources of illumination combine to make a new color, as when mixing lights. If light A and light B are both reflected from a surface to the eye, the colors of those two lights add together.
What is a subtractive color mixture?
A subtractive color mixture is when one source of illumination is subtracted from another, as when tow color filters are placed in front oa light source or when pigments are mixed. if pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remainder contributes to the perception of color.
What happens if you shine blue and yellow lights on the same patch of paper?
The wavelengths will add, producing an additive color mixture. Since yellow is equivalent to a mix of long and medium wavelengths, and blue consists of short wavelengths,the two lighs will produce a mixture of short, medium , and long wavelengths. The resulting mixture will therefore look white.
What does a color with zero saturation look like?
A color with zero saturation looks white.
What is the Young-Helmoholtz theory?
The trichromatic color theory.
How is the LGN important to color perception?
The LGN is a structure int he thalamus of the brain that receives input from the retinal ganglion cells and has input and output connections to the visual cortex. Some of its cells are maximally stimulated by spots of light, which are critical to color perception.
What is a color-opponent cell?
A color-opponent cell is a neuron whose output is based on a difference between sets of cones.
What are the opponent color sets in opponent color theory?
Red/green, blue/yellow, and black/white
What is a unique hue?
A unique hue is a color that can be described with only a single color term. Red is an example of a unique hue, as opposed to orange, which can be described as a compound (reddish yellow).
What is a negative afterimage?
A negative afterimage is a type of afterimage whose polarity is the opposite of the original stimulus. For instance, light stimuli produce dark negative afterimages. Colors produce complimentary after images. Red produces green, yellow produces blue etc. The negativity of the afterimages arises from the color-opponent cells.
What happens if the red/green and blue/yellow mechanisms are at their neutral points?
The stimulus will appear achromatic, no color..
How is someone colorblind?
Color-anomalous individuals cannot make abnormal discrimination based on wavelength. Cone monochromats are individuals with only one cone type, and therefore they cannot discriminate different colors, leading them to be truly colorblind.
What is color constancy?
Color constancy is the tendency of a surface to appear the same color under a fairly wide range of illuminants.
Why is luminance important for color constancy?
Luminance tends to be change abruptly between surfaces and gradually within surfaces, so surface boundaries are an important physical constraint for achieving color constancy. Shadow boundaries are also an important for for constancy.
What is an Isosensitivity (ROC) curve?
The Isosensitivity curve tells us about a person's sensitivity to a stimulus. When the slope=1, it means that the person had zero sensitivity. If the curve is slight curved above m=1, then the person is moderately sensitive. If the curve looks like an inverse parabola then the person is extremely sensitive.
What is the order of stimuli perception to action potential?
Photoreceptors-->horizontal/amacrine cells-->bipolar cells--> ganglion cells--> optic nerve fiber
What are simple cortical cells?
Simple cells have on and off areas, except not in a center-surround configuration. These cells respond best to bars of light.
What are complex cortical cells?
Complex cells respond best to bars of light moving in specific direction.
What role do feature detectors play in perception?
The receptive fields have become more and more specialized. They respond only to specific features of the visual stimulation. LGN,simple, complex, and hypercomplex cells are feature detectors.
What is Lateral Inhibition?
when the output of some receptors inhibits the neighboring receptors.
What are Mach Bands?
Mach bands are regions of perceived color differences. They enhance the differences between two neighboring regions. They can cause distortions that are not real. But, they help you to detect objects that may fade into the background
How does lateral inhibition apply to the Hermann grid?
You see false grey spots at the intersections of the black squares. These are caused by lateral inhibition.
Neural Circuit math equation
What are the physical parameters of light?
Wavelength, intensity, and spectral composition.
What are the psychological parameters of light?
hue, brightness and saturation
What is the hue, saturation, and brightness model?
A color circle that represents hue and saturation. The outer edge of the circle has the most saturated colors, closer to the center represents the low saturated colors. A slider allows you to vary the brightness of the color.
What is the Benham's top illusion?
Causes you to perceive colors that are not actually present. Cone selective neurons convey information about both color and luminance contrast, which causes them to be confounded.
What is dichromatism?
A common form of colorblindness. One of the wavelength specific cones is missing.
What is the absolute threshold?
The minimum intensity of stimulation required to produce a sensation
What is the difference threshold?
The minimum difference intensity between two stimuli that can be detected.
What is Weber's law?
JND= a constant proportion of the intensity of the standard.
What is Fechner's law?
Equal increments in physical intensity produce smaller and smaller increments in perceived magnitude.
What is Steven's law?
a power law