Sensation and Perception; Memory and forgetting Flashcards
What is sensation?
The activation of the sense organs by a source of physical energy (stimulus)
What is perception?
The sorting out, interpretation, analysis, and integration of stimuli carried out by the sense organs and brain
What is a stimulus?
Any passing source of physical energy that produces a response in a sense organ
What is an absolute threshold?
- Defined as the lowest intensity at which a stimulus can be detected (50 percent of the time).
- The lower the absolute threshold, the greater the sensitivity.
What is a difference threshold?
- The smallest level of added (or reduced) stimulation required to sense that a change in stimulation has occurred
- Just noticeable difference (JND)
- Weber’s law: A just noticeable difference is a constant proportion of the intensity of an initial stimulus
What is a just noticeable difference (JND)?
- The smallest difference between two stimuli that people can perceive (50 percent of the time).
- Weber’s law states that the difference threshold, or JND, is directly proportional to the magnitude of the stimulus with which the comparison is being made and can be expressed as a Weber fraction.
- Weber’s law breaks down at extremely high and low intensities of stimulation, but holds up reasonably well within the most frequently encountered range.
What is Weber’s Law? Provide an example.
Weber’s law states that the difference threshold, or JND, is directly proportional to the magnitude of the stimulus with which the comparison is being made and can be expressed as a Weber fraction.
Eg: Candle of 100 lumens
You are able to detect a change of 5 lumens
Proportional Change
5/100 = .05 = 5%
Candle of 500 lumens
How many lumens have to increase for you to detect a change?
500 lumens x 5% = 25 lumens
Total lumens = 525
What is sensory adaptation?
Turning down our responses. Adaptation is an adjustment (reduction) in sensory capacity after prolonged exposure to unchanging stimuli
Cornea
the transparent cover in the front of the eye and is responsible for about 80% of focusing the image
Lens
focuses the image by changing its shape depending on the distance of the object to the eye. Primarily used to focus close objects (less than 20 feet, 6 meteres)
Cillary muscles
focus the lens
Pupil
the opening that allows light to enter the eye
Iris
controls the size and diameter of the pupil
Retina
the back of the eye that contains the photoreceptors (rods and cones)
Fovea
a part of the eye which contains only cones and is where the visual image is focused. Therefore, this area has high visual acuity.
Blind spot
where the retina is connected to the optic nerve. Because there are no rods or cones here, it produces a blind spot. The optic disk, where the optic nerve exits the eye, has no receptors and produces a blind spot
What are rods and cones? What is the primary purpose of each?
Cones and rods are photoreceptors that can detect light. They have a pigment which is involved in a chemical reaction that signals the photoreceptor (neuron) to fire in response to certain wavelengths of light. There are many more rods (120 million) than cones (5 million) in the eye.
Cones are shaped like cones and are responsible for detecting colour. The fovea in the center of the eye only contains cones and has high visual acuity.
Rods are shaped like rods and are able to operate in low light, but do not see in colour.
What is feature detection in the context of neurons involved in sensory processing?
Feature detectors are specialized neurons that fire only when a very specific stimuli is present. For example, there are feature detectors that only fire for stimuli that contain a right angle, or are round, or are straight, or for lines that are slanted a certain number of degrees to the left or right, or lines that are oriented a certain way that are moving in a particular direction.
What is the trichromatic theory of colour vision?
Young-Helmholtz trichromatic theory (three types of cones):
The Young-Helmholtz trichromatic theory proposed three different receptors, one for blue, one for green, one for red.
The ratio of activity in the three types of cones yields our experience of a particular hue, or color.
The activity (rate of firing) for each receptor is dependent on the wave-lengths of light that reach the eye.
What is the opponent-process theory of colour vision?
Hering’s opponent-process theory (red-green and blue-yellow cones):
Hering’s opponent-process theory also assumed that there are three different receptors: one for blue-yellow, one for red-green, one for black-white.
Each of the receptors can function in two possible ways, depending on the wavelength of the stimulus.
Again, the pattern of activity in the receptor yields our perception of the hue.
How does the opponent process theory explain afterimages?
Colour Vision Theory: Remarkably, both theories are correct!
Trichromatic colour detection occurs first and then opponent process. In other words, they work together to help us perceive colour.
Afterimages
If you stare at an image for a period of time and then immediately look at a white surface, you will see an image of that object, but in different colours. The image you see when looking at the white surface is called an afterimage. Afterimages can be explained by the opponent-process theory of colour vision.
The cones contain photoreceptors which are pigments that result in a chemical reaction when light of certain wavelengths strike the cone. This chemical reaction signals the receptor to fire.
After awhile though, the ability of the photoreceptor to produce the chemical reaction to signal the receptor to fire diminishes and eventually stops. The photoreceptor needs to recover before it can fire again.
So, when you stare at an image, you are exhausting the photoreceptors detecting the colours of that image and due to the exhaustion can no longer fire.
If you turn away from the image and then look at a white surface, your eye is receiving light from across the entire colour spectrum (remember, white light contains all the wavelengths of the entire visible light spectrum).
However, some of the photoreceptors in our eye because they were exhausted looking at the image cannot fire at certain wavelengths, therefore, they cannot signal that they are receiving that portion of the light spectrum represented by the white light. This means that only one half of the photoreceptors responsible for triggering a particular opponent-neuron are firing. Because the opponent neuron only receives the messages from one half of the relevant photoreceptor neurons, it will fire accordingly.
Because the photoreceptors do recover fairly quickly, the afterimage will not last very long.
Example: If you stare at a blue image, you will exhaust the photoreceptors that detect blue. Then, if you look at a white image, the photoreceptors that detect blue will not fire, but those that detect yellow will fire. Therefore, the blue-yellow opponent neuron will only receive messages from the photoreceptors that are detecting yellow and none from the photoreceptors that detect blue. As a result, the opponent neuron will signal that it is seeing yellow. The afterimage does not last too long, because the blue photoreceptors will recover fairly quickly, and therefore, be able to detect the blue wavelengths contained within the white light spectrum.
What element of a sound wave determines pitch? Loudness?
Amplitude determines
intensity (loudness) (dB)
Frequency (Hz)
determines pitch (tone)
What is the place theory of hearing in terms of detecting different levels of pitch?
Place theory of pitch perception:
The specific point in the cochlea where the fluid wave peaks and most strongly bends the hair cells serves as a frequency coding cue
What is the frequency theory of hearing in terms of detecting different levels of pitch?
Frequency Theory of Pitch Perception:
The entire basilar membrane vibrates according to the frequency of the sound wave. Nerve impulses sent to the brain match the frequency of the sound wave.
Which theory of hearing is better?
Both Frequency and Place Theories are applicable in their own ways.
At low frequencies:
- Frequency Theory best explains sound wave frequency coding.
At higher frequencies:
- Place Theory best explains sound wave frequency coding.
At middle frequencies:
- Both processes are incorporated in sound wave frequency coding.
What is top-down processing? Provide an example.
Top-down processing
Perception that is guided by higher-level knowledge, experience, expectations, and motivations. Top-down processing is illustrated by the importance of context in determining how we perceive objects. For example, top down processing of an A requires that you know a language that uses the letter “A” and that you have knowledge of the alphabet. Next, you recognize that the shape is in the context of words, and therefore, likely is a letter.
What is bottom-up processing? Provide an example
Bottom-up processing
Perception that consists of the progression of recognizing and processing information from individual components of a stimuli and moving to the perception of the whole. For example, bottom up processing of an A first requires you to notice that there are three objects that have straight edges. Next, you need to notice that the objects touch one another. Then, you need to notice that they touch with an apex on top and that two of the objects extend at an angle and the third object is oriented differently between the two lines and is roughly in the middle of the figure.
What are visual illusions?
Usually two dimensional pictures that the brain perceives differently than the objective reality that is represented.
Often called optical illusions, but that label is a misnomer, the optical system is not “fooled”, but rather our interpretation of the picture or object is “incorrect”.
How can we use visual illusions to understand the visual system? Why Are Visual Illusions Important for Learning About and Understanding the Visual System?
The visual system has to contend with interpreting a three dimensional world with a two-dimensional image of the world cast upon the retina. Visual illusions are interpreted as if they come from a three dimensional world. If we can cause the visual system “misinterpret” a two dimensional representation of the world, we can then examine the elements of the picture and determine what information the visual system may have been using and how.
And, we can use our understanding of how the visual system works to create even better and more interesting visual illusions.
What are the Gestalt laws (principles) of organization?
Gestalt Principles of Perceptual Organization
Organizing the separate parts of our perceptual field into a unified and meaningful whole
Gestalt perceptual laws
A series of principles that describe how we organize bits and pieces of information into meaningful wholes.
Gestalt is the German term for “pattern”, “whole”, or “form”.
Pragnänz
the idea that we will perceive and interpret things in their simplest form.
Proximity
Objects that are closer together are perceived as belonging together
Similar Colour
Objects that are of a similar colour are perceived as belonging together
Similar Size
Objects that are of a similar size are perceived as belonging together
Common Fate
Objects that move together are perceived as belonging together.
Good Continuation
Straight or curving lines are perceived as belonging together and they tend to be perceived in such a manner as to follow the smoothest path
What is Kanizsa’s triangle?
Kanizsa triangle is perhaps the most famous example of illusory contours.
Note that although you can easily see a white triangle in the middle of the image, there really is not one there. Also, many people see the white triangle as brighter (whiter) than the surrounding white.
What is a Penrose Triangle?
The Penrose Triangle is likely the first impossible figure and was first proposed by ‘The Father of Impossible Figures’ Oscar Reutersvärd.
Describe the model of working memory.
The set of temporary memory stores that actively manipulate and rehearse information Central executive processor
Visual store
Verbal store
Episodic buffer
