1)      Describe the anatomy of the human eye, including a discussion of the main functions of its major parts. Use a drawing to show where these parts are located.

a.       Outer portion called the cornea (used to end light rays as they enter the eye). Iris (changes size of the pupil in order to control the amount of light entering the eye), Lens (focuses the light rays entering the eye), Pupil (allows light to enter into the eye), Retina (has photo receptors, rods and cones, on it which convert the light into neural impulses through the process of transduction), fovea (where the majority of the rods are located and is used for visual acuity), Optic nerve (carries the neural impulses created by the photo receptors to the brain. Where the optic nerve exits the eye there are no receptors, this causes a blindspot)

1)      Describe the similarities and differences between the rods and the cones, including their sensitivity to light and color, and their distribution on the retina.

a.       Similarities – Both photoreceptors which are found in the retina. Both exhibit Transduction, which is the transformation of light into electrical impulses. They both also undergo dark adaptation.

b.      Differences – Different shapes. Rods undergo dark adaptation slower, but have greater sensitivity overall and become bleached more in bright light, and thus take longer to reach their full potential of dark adaptation, while the Cones undergo dark adaptation quickly.

c.       Rods – Highly sensitive to light. As such they are used for night vision. They are largely distributed throughout the eye, except in the fovea, which has almost none on it. Not sensitive to red light. Many rods are chained together onto single ganglion cells, they have greater convergence. This gives them increased sensitivity to light, but this comes at the cost of acuity in what they detect.

d.      Cones – Less sensitive to light. Used in day vision as well as detail vision. Sensitive to red light. They are distributed lightly throughout the eye, but on the fovea that are highly concentrated. Cones are often connected to ganglion on a 1-to-1 basis. This gives them great ability to provide accurate detail as to the positioning of the source of the stimuli, which is why they provide greater acuity.

1)      Discuss the four major types of eye movements in visual perception and describe their functions.

a.       Pursuit movements – This type of movement is used in the tracking of objects. They are relatively slow and smooth in their movement and allow for the maintaining of visual contact with a moving object, keeping its image on the fovea.

b.      Saccadic Movements – These are rapid eye movements which allow for the quick shifting of attention from one part of the visual field to another. Most often triggered by some meaningful stimuli which occurs in the perhiphery. While these movements are underway you are rendered ‘blind,’ by Saccadic suppression, to the movements, such as when a person looks in the mirror and is unable to see their eyes move when they consciously shift their attention.

c.       Convergent movements – These movements are when the eyes rotate inwards and outwards as is necessary in order to track an object in terms of depth. As the object moves further away the eyes rotate outwards, as it approaches they rotate inwards.

d.      Micro-Saccades – These are small, rapid, jerky movements which the eye unconsciously makes in order to ‘refresh’ visual information so that objects being observed do not fade from the visual field. This is because as time goes on, and visual information appears to not change, the visual system phases out the information. 

1)      Explain how lateral inhibition functions in the visual system, and describe its two major benefits.

a.       May help to draw a diagram for this question.

b.      When you stimulate a group of cells, neighboring cells will inhibit each other.

c.       How it functions: When receptor cells in the eye, as we are talking about the visual system, are being uniformly hit with the same intensity of light, some receptors will essentially ‘shut-down’ due to inhibitory signals sent by adjacent neurons, and the remaining ones will ‘share’ the information that is being received.

d.      Major benefits: 1) Conservation of energy / Economy – It allows for the receptors to save energy if there is nothing important being received. 2) Enhancing of contours. This occurs when you are moving from a darker field (less lateral inhibition) to a lighter field (More lateral inhibition). As you move from one field to the next, the area between it will show a variation in intensity (Mach Bands result from this). This is because as you are moving from the darker to the lighter, the inhibitory signals being sent are begin to be overcome; the signals will increase because excitation from brightly lit photoreceptors is not completely offset by inhibition from the dimly lit photoreceptors.

1)      Describe the major differences between center-surround ganglion cells, simple cells in the visual cortex, and complex cells in the visual cortex.

a.       Center-surround ganglion cells– This primarily responds to round points of light. The receptive field in which the two parts, the center and the surround, react opposite of each other in regards to stimulation received on that area. For example, Excitatory-center Inhibitory-surround set up, when stimuli (like light in this case) hit the center of the field, the ganglion cells fire rapidly. However, when that stimuli hits the surrounding area, the firing decreases, it becomes inhibited. These networks of cells are located on the retina.

b.      Simple cells – Side-by-side structures located in the Striate Cortex. Selectively respond to specific orientations of bar-shaped features. Similar to Center-surround system in that they have receptor fields which become exited in one way and inhibited in another. Specifically for these though, the fields are excited by specific orientation of bar-like features. As the bar moves from the excitatory orientation, in which the neuron is reacting, it moves into the inhibitory orientations in which the neuron slows or ceases reaction.

c.       Complex cells – Found deeper in the Striate Cortex. Like simple cells, these react to specific orientations of bar-shaped features. However, unlike simple cells, most of these complex cells will only respond to specific orientations of bar shaped features that move across the entire receptive field. Further, they will respond best or only to specific directions of movement of the correctly oriented bar-shaped feature. These also respond better to specific lengths of the bar-shaped features.

1)      Compare two theories of the neural basis of object recognition, one based on bar-shaped feature detectors and the other based on spatial frequency analysis.

a.       Bar-shaped detector theory – Start with bar-shaped feature detectors and from that construct increasingly complex detectors as you group the detectors together. This creates increasingly complex detectors as you move further up the visual system, such as a square detector, a house detector, and so on.

b.      Spatial frequency – This expands the entire field of vision and detects what spatial frequencies are present and from these combine to form whatever object we need. This also allows for blurring of an object to not affect the recognition of the object entirely. Such blurring causes a considerable problem for bar detectors, but even low frequencies allow for recognition of the object.

1)      Discuss evidence for dissociations in the visual system between our perception of what an object is and our perception of where it is located.

a.       Dissociations in the visual system come from the idea of the two pathway system. They are separate in their function, allowing for one to be damaged while the other stays functional. Essentially one path way deals with the perception of what the object is while the other pathway deals with where the object is. Specifically the Ventral pathway deals with the identification, or ‘what’ of an object. The Dorsal pathway deals with the location of or ‘where’ of an object. It should be noted that the Dorsal pathway is often considered the ‘how’ pathway as it appears to deal with the manner in which to reach and use objects, rather than purely locate them.

b.      Evidence for these dissociations comes from testing on primates as well as studies of brain damaged individuals. In the case of primates they are tested in regards to locating food, either by object recognition (the ‘what’) or landmark association (the ‘where’ part of the equation), ablation is then used to destroy targeted areas of the brain and they are retested. It was found that yes, in expected in cases of primates with damaged Dorsal pathways they could use landmark recognition to locate food, but encountered difficulty in locating food via object recognition. The opposite was found in those with damaged Ventral pathways, as they were able to recognize objects (what), but not landmarks (where).

1)      What are the main advantages and limitations of the template, feature description, and structural models of pattern recognition?

a.       Template: Recognition of an object by matching to an existing mental template which is stored in the mind.

                                                               i.      Advantages: Recognition is quick and easy cognitively speaking; so long as the template exists in the mind. Little effort is required when a matching set of features is detected and set within the template.

                                                             ii.      Disadvantages: This essentially requires an infinite number of templates to be stored at any given time as a single object may have varying forms, with each form or shape requiring a separate template in order to be recognized. This also means that there is an ignoring of the intuition that an object is made up of smaller parts.

b.      Feature description / Feature List Model: Essentially breaking down an object into a specific set of characteristic features which are identified and then placed together in order to recognize the object.

                                                               i.      Advantage: It no longer requires an infinite number of templates, as the list of features can be applied to numerous types of the same object. (i.e. Different hand written versions of the letter ‘A’ can all be identified by the same set of features which exist within each.) It is a much more economical model.

                                                             ii.      Disadvantage: Ambiguity can crop up in the detection of features, especially with two-dimensional objects. This ambiguity can cause the features to be interpreted multiple ways, and thus increase chances of misidentification.

c.       Structural Model: States that recognition is based upon detection of structures which make up the object as a whole (“Geons”). These geons are the basic structures which compose an object and placing them together allows for the recognition of it.

                                                               i.      Advantages: This lacks the problems of ambiguity which Feature description can result in.  Also economy is an advantage as a small number of Geons (36, according to Biederman) can be used to construct just about any object that may be observed. It does not require an infinite number of templates, nor a long list of features to be put together.

                                                             ii.      Disadvantages: If an object has poorly defined or unusual structure it can be difficult to identify it. This can require that some objects, perhaps unsymmetrical in nature, be observed from particular angles in order to be correctly identified.  

a.       There are a number of Gestalt principles which demonstrate how the visual system operates.

                                                               i.      Law of simplicity – This is a principle which states that the mind has a tendency to come up with the simplest explanation for a visual pattern which is presented. Ex: A person is out hiking and notices a something that appears to be Á behind a tree. It could be that the tree simply has a very unusually shaped trunk, but the law of simplicity makes it much easier to simply see it as an object which is obscured by the tree rather than being a part of it.

                                                             ii.      Law of similarity – All other things being equal, the mind will group things that are similar together. Ex: Continuing with the previous example. The object or objects obscured by the tree appear to have the same color and texture, thus the two separate pieces of information, separated by the tree trunk, are grouped together.

                                                            iii.      Law of good continuation – When presented with a patter, the mind will perceive it in the simplest way which provides for the continuation of the pattern. Ex: Again, with the obscured object or objects behind the tree. From the observer’s position, there appears to be a clear line of continuation from one part of the visual information to the next on the other side of the tree. So again, rather than perceiving the object as possibly being separate, it is perceived as having continuation behind the object.

                                                           iv.      Law of familiarity – Things that are familiar, or appear familiar, tends to stand out against the background. Ex: Back to the object behind the tree. Perhaps the shape of the object, or objects, has a familiar shape. Maybe it looks like a dog. As such, the object stands out more clearly from the background and after recognizing the shape as that of a dog, it becomes exceedingly difficult to not perceive the shape as a dog.

                                                             v.      Law of common fate – Objects which are moving together are grouped together. Ex. Finally we get away from the object behind the tree. This is because the hiker approaches the object and finds that no, it is not a dog, just two old, funny shaped stumps. But this investigation causes birds nesting in the tree to scatter into the sky. Common fate dictates that as the birds are all flocking together in one direction that they compose a single group. If some of the birds start heading in a different direction those birds are grouped separately from the initial unit, and two groups are considered as being seen.

1)      What is figure-ground segregation, and why is it an important process in the human visual system? What factors help us to distinguish figure from ground?

a.       Figure-ground segregation is the visual system’s ability to distinguish an object that is in the foreground and features that exist in the background. It is important in that it allows for us to distinguish these objects as being separate from features in the background. However, in cases where there is ambiguity, it becomes difficult to differentiate. In these cases factors such as: Depth cues – where things that are closer are recognized as being in the foreground; Texture – Objects in the foreground tend to ehibit more texture and detail; Symmetry – where things that are more symmetrical are recognized as being in the foreground; Lower appearance in the visual field and taking up a smaller area of the visual field; Increased horizontal and vertical features recognized; and Familiarity with an object, as things which are familiar tend to stand out from the background; are all used to assist in distinguishing the figure from the background.

{  Both photoreceptors which are found in the retina.

{  Both exhibit Transduction, which is the transformation of light into electrical impulses.

{  They both also undergo dark adaptation.

• DIFFERENT SHAPES
• RODS UNDERGO DARK ADAPTATION SLOWER
• BUT HAVE A GREATER SENSITVITY OVERALL AND BECOME BLEACHED MORE IN BRIGHT LIGHT
• THUS TAKE LONGER TO REACH THEIR FULL POTENTIAL OF DARK ADAPATION
• CONES UNDERGO DARK ADAPTATION QUICKLY

1. PURSUIT MOVEMENTS
2. SACCADIAC MOVMENTS
3. MICRO SACCADES MOVEMENTS
4. CONVERGENT MOVEMENTS

What type of eye movements are underway when you are rendered "blind" by ______ suppression?

example) to the movements such as when a person looks in the mirror and is unable to see their eyes move when they consciously shift their attention.

Saccadic Movements

Saccadic is the fill in the blank for saccadic supression

1. receptor cells in the eye are being uniformly hit with the same intensity of light........
2. causes some of the receptors to essentially "shut down" due to the inhibitory signals sent by adjacent neurons......
3. the receptors that dont shut down, will share information that is being recieved.

1. CONERVATION OF ENERGY/ AND ECONOMY'
2. ENHANCING CONTOURS

This occurs when you are moving from a darker feild (less lateral inhibition) to a lighter feild more lateral inhibition.

when you move from one feild to the next, the are between it wil show a variation in intensity (mach bands result from this)

this is because as you are moving from the darker to the lighter, the inhibitory signls being sent are being overcome.

the signals will increase because excitation from brightly lit photoreceptors is not completely offet by inhibition from dimly lit photoreceptors

1. center-surround ganglion cells
2. simple cells
3. complex cells

What cell in the visual cortex is {  Like simple cells, these react to specific orientations of bar-shaped features?

{  Start with bar-shaped feature detectors and from that construct increasingly complex detectors as you group the detectors together.

{  This creates increasingly complex detectors as you move further up the visual system, such as a square detector, a house detector, and so on.

{  This expands the entire field of vision and detects what spatial frequencies are present and from these combine to form whatever object we need.

{  This also allows for blurring of an object to not affect the recognition of the object entirely.

{  Such blurring causes a considerable problem for bar detectors, but even low frequencies allow for recognition of the object.

  Such blurring causes a considerable problem for bar detectors, but even low frequencies allow for recognition of the object.

{  This also allows for blurring of an object to not affect the recognition of the object entirely. 

{  This expands the entire field of vision and detects what__________are present and from these combine to form whatever object we need.

mach bands

related to lateral inhibtion

§  Colors of varying intensity lined up beside each other

§  Darker colors appear darker because of increased inhibition activity

Lighter colors appear lighter because of decreased inhibition

§  Increased lateral inhibition caused by bright backgrounds make an object within that field appear darker

§  Decreased lateral inhibition caused by darker backgrounds makes an object within that field appear brighter

§  i.e. a grey ball appears brighter in front of a dark background, but move it in front of a white back ground it appears darker, even though its color has not changed

§  Economy of vision

§  Contour enhancement