Sensation & Perception Exam 4 Study Guide

Characteristics of optic flow

1. The flow is more rapid near the moving observer 2. There is no flow at the destination toward which the observer is moving. 3. Produces invariant information. Key invariants are the properties that remain constant as an observer moves through the environment. Optic flow provides invariant information because it occurs no matter where the observer is, as long as he or she is moving. The focus of expansion is also invariant because it is always centered on where the person is heading.

Affordances

Objects have this property. It is information that indicates what an object is used for. "The affordances of the environment are what it offers the animal, what it provides for or furnishes." Ex: a chair or anything that is "sit-on-able", affords sitting. *this means that our responses to an object does not only include physical properties, such as shape, size, color, and orientation, that might enable us to recognize the object; our response also includes information about how the object is used. Aka "potential for action".

Motion aftereffects

Occur after viewing a moving stimulus for 30-60 seconds and then viewing a stationary stimulus, which appears to move. One example is the : Waterfall illusion: If you look at a waterfall for 30-60 secs, and then look off to the side at part of the scene that is stationary, you will see everything you are looking at - rocks, trees, grass - appear to move up for a few seconds. Motion aftereffects can also occur after viewing other kinds of motion. Ex: viewing a rotating spiral that appears to move inward causes apparent expansion of a stationary object.

Image displacement signal (IDS)

Occurs when a stimulus is displaced across the retina. According to corollary discharge theory, when the IDS reaches the comparator, the comparator sends a signal to the brain that results in the perception of motion.

Induced motion

Occurs when motion of one object (usually a large one) causes a nearby stationary object (usually smaller) to appear to move.

Physiology of Reaching & Grasping - neurons in the parietal lobe/goal-directed movements

One of the first discoveries made by these researchers was that some neurons in the parietal cortex that were silent when the monkey was not behaving began firing vigorously when the monkey reached out to press a button that caused the delivery of food. The most important aspect of this result is that the neurons fired only when the monkey was reaching to achieve a goal such as obtaining food. They didn't fire when the monkey made similar movements that were not goal-directed. Ex: no response occurred to aggressive movements, even though the same muscles were activated as were activated during the goal-direct movements.

Perceiving biological motion

One reason we are particularly good at perceptually organizing the complex motion of an array of moving dots into the perception of a walking person is that we see biological motion all the time. Every time you see a person walking, running, or behaving in a way that involves movement, you are seeing biological motion.

Important things about studying perception

One task is to determine what information is available for perception. This is what Gibson accomplished in identifying information such as optic flow and the focus of expansion. Another is to determine what information is actually used for perception. Optic flow can be used, but other sources of information are probably used as well. Ex: flow information, visual direction strategy, auditory information.

Motion helps us understand events in the environment

Our ability to use motion info to determine what is happening is an important function of motion perception that we generally take for granted. Motion perception is also essential for our ability to move through the environment.

Illusory motion

Perception of motion when there actually is none.

Reflectance curves

Plots of the percentage of light reflected versus wavelength - for a number of objects. Black and white paper both reflect all wavelengths equally across the spectrum, but blue, green, and yellow paint and tomato reflect some wavelengths but not others.

Local disturbance in the optic array

Portions of the optic array become covered as someone walks by and then are uncovered when he moves on. OR a local disturbance happens when one object moves relative to the environment, covering and uncovering the stationary background.

Ecological approach to perception

Proposed by J.J. Gibson, it focuses on how perception occurs in the environment by (1) emphasizing the moving observer - how perception occurs as a person is moving through the environment - and (2) identifying information in the environment that the moving observer uses for perception.

Motion perception has a number of different functions

Providing us with updates about what is happening to helping us perceive things such as the shapes of objects and people's moods. Perhaps, most important of all, especially for animals, the perception of motion is intimately linked to survival.

The senses do not work in isolation

Rather than considering vision, hearing, touch, smell, and taste in isolated categories, we should consider how each provides information for the same behaviors. -ex: balance. our ability to stand up straight, and to keep your balance while standing still or walking, depends on systems that enable us to sense the position of our body. These systems include the vestibular canals of your inner ear and receptors in the joints and muscles. However, Gibson argued that vision also plays a role in keeping our balance. See what happens when visual information isn't available (closing eyes while trying to balance). Became more difficult. Vision provides a frame of reference that helps the muscles constantly make adjustments to help maintain balance.

One of the major actions we take

Reaching to pick up something. One of the characteristics of reaching and grasping is that it is usually directed toward specific objects, to accomplish a specific goal.

Basic colors

Red, yellow, green, and blue.

Comparator

Relays info back to the brain that the eye is moving.

Navigating through the environment - testing Gibson's ideas

Research on whether people use flow information has asked observers to make judgements regarding their heading based on computer-generated displays of moving dots that create optic flow stimuli. The observer's task is to judge, based on topic flow stimuli, where he or she would be heading relative to a reference point such as a vertical line. *Although research has shown that flow information can be used to determine heading, there is also evidence that people use other info as well.

Real motion neuron

Responds only when the stimulus moves and doesn't respond when the eye moves, even though the stimulus on the retina - a bar sweeping across the cell's receptive field - is the same in both situations. This real motion neuron must be receiving info like the corollary discharge, which tells the neuron when the eye is moving. Real motion neurons also have been observed in many other areas of the cortex and more recent research has begun to determine where the corollary discharge is acting in the brain.

Extrastriate body area (EBA) and fusiform face area (FFA)

Specialized to respond to bodies and faces.

Attentional capture

The ability of motion to attract attention. This effect occurs not only when you are consciously looking for something, but also while you are paying attention to something else.

Focus of expansion (FOE)

The absence of flow at the destination point. Because the FOE is centered on the observer's destination, it indicates where the observer is heading.

Gradient flow

The different speed of flow - fast near the observer and slower farther away. The gradient of flow provides information about the observer's speed.

Global optic flow

The fact that everything moves at once is called global optic flow; this signals that Maria is moving but that the environment is stationary.

What's the evidence that the mirror neurons are actually involved in helping "understand" an action?

The fact that the response occurs when the experimenter picks up the food with his hand but not with the pliers argues that the neuron is not just responding to the pattern of motion.

Aperture problem

The fact that viewing only a small portion of a larger stimulus can result in misleading information about the direction in which the stimulus is moving.

Representational momentum

The idea that the motion depicted in a picture tends to continue in the observer's mind. Representational momentum is an example of experience influencing perception because it depends on our knowledge of the way situations involving motion typically unfold.

Motion of a Bar across an aperture

The movement of an edge across an aperture occurs perpendicular to the direction in which the edge is oriented. Because the pencil in our demonstration was oriented vertically, motion through the aperture was horizontal. Because motion of the edge was the same in both situations, a single directionally selective neuron would fire similarly in both situations, so the activity of the neuron would not provide accurate information about the direction of the pencil's motion.

Optic flow - as you move

The movement of elements in a scene relative to the observer.

How do neurons called mirror neurons respond when a person perceives an action and when the person watches someone else perceive the same action?

The neuron's response to watching someone else perform the action is the same as the response that occurs when the observer performs the action. This means that one function of the mirror neurons might be to help understand another person's actions and react appropriately to them.

Summary of corollary discharge theory

The perception of movement occurs if the comparator receives either (1) a signal that the eye is moving (CDS) or (2) a signal that an image is being displaced across the retina.

Selective reflection

The property of reflecting some wavelengths more than others

Color and wavelength

The spectrum stretches from short wavelengths (400 nm) to long wavelengths (700 nm), and bands of wavelengths within this range are associated with different colors. Wave lengths from about 400-450 nm appear violet; 450-490 nm, blue; 500-575 nm, green; 575-590 nm, yellow; 590-620 nm; orange; and 620-700 nm. red.

Optic array

The structure created by the surfaces, textures, and contours of the environment.

Solving the aperture problem

The visual system appears to solve this by pooling the responses of a number of neurons like our complex cell. One place this may occur is the medial temporal (MT) cortex, a nucleus in the dorsal (where or action) stream, which contains a large number of directionally selective neurons and which we will see is important for movement perception. -- also by using information from neurons in the striate cortex that respond to the movement of the ends of objects

The color of objects are largely determined by?

The wavelengths of light that are reflected from the objects into our eyes.

What happens if both a CDS and an IDS reach the comparator simultaneously?

This would occur if you were to move your eyes to inspect a stationary scene. In this case, a CDS is generated because the eye is moving, and an IDS is generated because images of the scene are sweeping across the retina. According to corollary discharge theory, when both the CDS and IDS reach the comparator simultaneously, no signal is sent to the brain, so no motion is perceived.

How do films create movement from still pictures?

Through apparent motion. An observer perceives one stimulus moving back and forth smoothly between two locations, but there is actually no real motion between the stimuli.

Another way a neuron might indicate that the pole is moving up and to the right

Use info about the end of a moving object (such as the tip of the pencil) to determine its direction of motion. As it turns out, neurons that could signal this information, because they respond to the ends of moving objects, have been found in the striate cortex.

Movshon & Newsome (1992)

Used microstimulation to activate neurons in a column that responded best to a particular direction of motion while a monkey was judging the direction of dots that were moving in a different direction. When they applied the stimulation, the monkey suddenly its judgement toward the direction signaled by the stimulated neurons. The fact that stimulating the MT neurons shifted the monkey's perception of the direction of movement provides more evidence linking MT neurons and motion perception.

Some approaches to developing a prosthesis

Using signals from the motor cortex that normally would be sent to the muscles. -Leigh Hochberg & coworkers (2006) pg. 172 Another promising approach has been to use signals from the PRR.

Implied motion

When a still picture depicts a situation involving motion

Achromatic colors

When light reflection is similar across the full spectrum - that is contains no hue - as in white, black, and all the grays between these two extremes, we call those colors achromatic colors.

Chromatic colors or hues

When some wavelengths are reflected more than others.

What is the connection between perceiving and moving through the environment?

When you look out from where you are right now, all of the surfaces, contours, and textures as you see make up the optic array; if you get up and start walking, the changes that occur in the surfaces, contours, and textures provide information for perception. Also, we need to perceive to move, and we also need to move to receive.

Motion agnosia

When you lose the ability to perceive motion. Suffering a stroke that damaged an area of the cortex can cause this.

Motor signals (MS)

Your eyes move because motor signals are being sent from the motor area of your brain to the eye muscles.

Swinging room experiement

pg. 159

Driving Experiments - Land & Lee

pg. 160

Kenneth Britten and Richard van Wezel - monkey experiment & MST

pg. 161

Testing affordances by looking at the behavior of people with brain damage - Glyn Humphreys & Jane Riddoch

pg. 165

Guiseppi Di Pellegrino and coworkers (2005)

pg. 165-166

Jeffrey Calton & monkey experiments

pg. 166-167

Jason Connolly and coworkers (2003)

pg. 167

Andrea Pierno & coworkers (2006) Evidence for neurons that respond to other people's intentions to carry out an action

pg. 169

Beatriz Calvo-Merino & coworkersn (2005-2006) - Mirror neurons and experience

pg. 170

Controlling movement with the mind - moving a cursor on a computer screen

pg. 171-172

Axel Larsen & coworkers - comparing real and apparent motion

pg. 182

When we scan or walk through a room, the image of the room moves across the retina, but we perceive the room and the objects in it as remaining stationary. Why does this occur?

pg. 184

Christopher Pack & Richard Born (2001) - Evidence that the MT may be involved in pooling the responses from a number of neurons

pg. 186

William Newsome & coworkers (1989) - moving dots display

pg. 187

Lawrence Stark & Bruce Bridgeman (1983) - eyelid experiment

pg. 191

Emily Grossman & Randolph Blake - specialized area for biological motion

pg. 192 +193-94 (TMS stimulation)

Jennifer Freyd (1983) - implied motion experiment

pg. 194

Catherine Reed and Norman Vinson (1996) - effect of experience on representational momentum

pg. 194-195

James W. Tanaka and L. M. Presnell (1999)

pg. 203

What does someone who is "color-blind" see?

pg. 211

Why do we perceive blue dots when a yellow flash bulb goes off?

pg. 214

What colors does a honeybee perceive?

pg. 224

Mr. I

A painter who became color blind at the age of 65 after suffering a concussion in an automatic accident. His color blindness was caused by cortical injury after a lifetime of experiencing color, whereas most cases of total color blindness or of color deficiency (partial color blindness) occur at birth because of the genetic absence of one or more types of cone receptors.

Extinction

A person with extinction can identify a stimulus in the right or left visual field if just one stimulus is presented. However, if two stimuli are presented, one on the left and one on the right, these people have trouble detecting the object on the left.

How does the perceptual system indicate that the stimulus is moving, even though there is no movement on the retina?

According to corollary discharge theory, our perceptual system uses a signal called the corollary discharge to take into account the fact that the observer's eye is moving.

Corollary discharge theory

According to this theory, another neural signal, called the corollary discharge signal (CDS), splits off from the motor signal. The corollary discharge signal, which occurs anytime a motor signal is sent to the eye muscles, indicates that a signal has been sent from the brain to move to the eye. The corollary discharge signal reaches a hypothetical structure called the comparator. *If there is no movement of an image across the retina, but the comparator is receiving information indicating that the eye is moving, then the observer perceives motion

Real motion

Actual motion of an object. Ex: perceiving a car driving by, people walking, or a bug scurrying across a tabletop.

Functions of Color Vision

Adds beauty to our lives, but it also serves important signaling functions, both natural and contrived by humans. The natural and human-made world provides many color signals that help us identify and classify things. Color also helps facilitate perceptual organization, by which small elements become grouped perceptually into larger objects. Color perception greatly facilitates the ability to tell one object from another and especially to pick out objects within scenes, an ability crucial to the survival of many species. Additionally, enhances the contrast of objects that, if they didn't appear colored, would appear more similar.

When colored lights are superimposed - mixing lights

All of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed.

Visual direction strategy - walking experiments

An important strategy used by walkers that does not involve flow is this strategy. Observers keep their body pointed toward a target. If they go off course, the target will drift to the left or right. When this happens, the walker can correct a course to recenter the target.

Self-produced information - another basic idea behind the ecological approach

An observer's movement provides information that the observer uses to guide further movement.

Flow information not necessary

Another indication that flow information is not always necessary for navigation is that we can find our way even when flow information is minimal, such as at night or in a snowstorm.

How can we explain how neural firing signals the direction that an object is moving?

As the stimulus sweeps across the retina, it activates directionally selective neurons in the cortex that respond to oriented bars that are moving in a specific direction.

Saturation

Changing the intensity to make colors brighter or dimmer, by adding white. White is equal amounts of all wavelengths across the spectrum, and adding white decreases a color's saturation. Ex: adding white to the deep red at the top of the color circle makes it become pink, which is a less saturated (or desaturated).

Point-light walker stimuli

Created by Gunnar Johansson by placing small lights on people's joints and then filming patterns created by these lights when people worked and carried out other actions in the dark. When the person wearing the lights is stationary, the lights look like a meaningless pattern. However, as soon as the person starts walking, with arms and legs swinging back and forth and feet moving in flattened arcs, the lights are immediately perceived as being caused by a walking person. This motion of a person or other living organism is called : biological motion

Neural prostheses

Devices that substitute for the muscles that move. Signals from the brain are not sent to the muscles, but to a computer that transforms these signals into instructions to move the cursor, or in some cases, control a robotic arm that can grasp and manipulate objects.

Blind walking procedure - Jack Loomis & coworkers, pg. 160

Eliminated flow altogether. People observe a target object located up to 12 meters away, then walk to the target with their eyes closed. These experiments show that people are able to walk directly toward the target and stop within a fraction of a meter of it. Fact that the person stopped close to the target shows that we are able to accurately navigate short distances in the absence of any visual stimulation at all.

Problems remain to be solved before a device can become routinely available

Even under controlled lab conditions, using computer-analyzed brain activity to control movement is much less accurate and more variable than the control possible when signals are sent directly to the muscles. One reason for this variability is that signals are sent to the muscles in tens of thousands of neurons, and these signals contain all of the info needed to achieve precise control of the muscles. In contrast, researchers developing neural prostheses are using signals from far fewer neurons and must determine which aspects of these signals are most effective for controlling movement.

Physiological approach to motion perception

Focuses on determining the connection between neural firing and motion perception.

The perception of the point-light walker stimulus as a person is seen walking is an example of?

How movement can create perceptual organization, because the movement transforms dots that appear unrelated into a pattern that is almost immediately seen as a meaningful figure.

Bennett Berthenthal and coworkers

In a developmental study, they showed that infants as young as 4 months old sway back and forth in response to movements of a room, and that the coupling of the room's movement and the swaying becomes closer with age.

Cause of extinction

It is caused by a person's inability to direct attention to more than one thing at a time. Possibly damage to the parietal lobe.

Microstimulation

It's achieved by lowering a small wire electrode into the cortex and passing a weak electrical charge through the tip of the electrode. This weak shock stimulates neurons that are near the electrode tip and causes them to fire, just as they would if they were being stimulated by neurotransmitter released from other neurons.

The role of the MT cortex has been studied by determining how the perception of motion is affected by

Lesioning (destroying) some or all of the MT cortex or electrically stimulating neurons in the MT cortex. A monkey with an intact MT cortex can begin detecting the direction dots are moving when coherence is as low as 1-2%. However, after the MT is lesioned, the coherence must be 10-20% before monkeys can begin detecting the direction of motion.

Transcranial magnetic stimulation

More gentle and temporary method of disrupting brain activity. Possible to temporarily disrupt the functioning of a particular area by applying a pulsating magnetic field using a stimulating coil placed over the person's skull. A series of pulses presented to a particular area of the brain for a few seconds decreases or eliminates brain functioning in that area for seconds or minutes. A participant's behavior is tested while the brain area is deactivated. If the behavior is disrupted, researchers conclude that the deactivated area of the brain is causing that behavior.

Selective transmission

Most colors in the environment are created by the way objects selectively reflect some wavelengths. But in the case of things that are transparent, such as liquids, plastics, and glass, chromatic color is created by selective transmission, meaning that only some wavelengths pass through the object or substance.

Where is the comparator located?

Most likely not located in one specific place in the brain, but may involve a number of different structures. Similarly, the corollary discharge signal probably originates from a number of different places in the brain.

Specialization of mirror neurons

Most mirror neurons are specialized to respond to only one type of action, such as grasping or placing an object somewhere.

Parietal reach reguib

Neurons in the posterior parietal cortex that respond when a monkey is planning to reach, or is actually reaching constitute this region.

Mirror neurons - Giacomo Rizzolatti & coworkers (2006)

Neurons that respond both when a monkey observes someone else (usually the experimenter) grasping an object such as food on a tray and when the monkey itself grasps the food. They are called mirror neurons because the neuron's response to watching the experimenter grasp an object is similar to the response that would occur if the monkey were performing the action. Just looking at the food causes no response, and watching the experimenter grasp the food with a pair of pliers causes only a small response.

Optic flow neurons

Neurons that respond to optic flow patterns are found in the medial superior temporal area (MST)

Audiovisual mirror neurons - more evidence that mirror neurons are doing more than just responding to a particular pattern of stimulation

Neurons that respond to sounds that are associated with actions. audiovisual mirror neurons are located in the premotor cortex and they respond when a monkey performs a hand action and when it hears the sound associated with this action.