Week 9 Flashcards
What is psychophysics?
- Refers to psychological sensations of physical properties of the world
- Fechner and Von Helmholtz’s goal was to measure the relationship between the physical characteristics of the stimulus and the sensory experience
- Helped understand all of perception in terms of elementary sensation
What is the difference threshold?
- Just-noticeable difference between two stimuli
- In all sensory domains, the just noticeable difference threshold goes up as the intensity goes up
What is Fechner’s Law?
Each JND represents an equal step in the psychological magnitude of a sensation which means changes in stimulus can be compared across sensory domains
What is Steven’s Power Law?
The proposed relationship between the magnitude of a stimulus and its perceived intensity or strength
What is the absolute threshold?
- The minimum intensity of stimulation that must occur before we can experience a sensation
- Can only be detected 50% of the time
What are faint signals?
Stimuli not only depends on an individual’s sensitivity but also their expectations
What are Cognitive factors?
A individual’s ability to hear faint signals which involve thought processes, including changes in attention, expectation and alertness
What is response bias?
A person’s willingness to say yes or no with disregard to sensitivity
What is Signal Detection Theory?
Argues that there is no absolute threshold because what is measured as the absolute threshold changes based on the person’s ability to detect it against background noise
What is pitch?
- How high or low we believe a sound to be
o High cycling, changing and alternating frequencies are high pitches - Fundamental frequency is the lowest frequency of a periodic waveform
- Pitch is decoded when the cochlea breaks down sound into their component frequencies
- The presence of each frequency and its intensity are sent to the brain through individual fibres of auditory nerves
- Each nerve is most sensitive to a certain pitch
What is Tonotopic organization (place codes)?
- When frequencies are anatomically separated and organized in the ear
- Organization is maintained all the way to the primary auditory cortex
- Acts as a code which signals which frequencies are present in the sound
What are temporal codes?
- Used for lower-frequency sounds
- Able to be used up to frequencies of 5000 Hz
- Auditory nerve fibres fire quickly and in sync with a stimulating waveform
- Every time there is a compression in the sound wave, the hair cell depolarizes and an action potential is generated
What is the volley principle?
- When sounds have frequencies higher than 1000 Hz but lower than 5000 Hz, fibres take turns creating action potentials
- The sequence must be precise
What are temporal and place codes used for?
Place codes are used for high pitch noises whereas temporal codes are used for lower frequencies
What are complex sounds made of?
Complex sounds are made of multiple components
What is the fundamental frequency?
The lowest frequency component of a sound
What are the elements of sound?
They have the fundamental frequency, harmonics (all of the other components of sound which are multiples of the fundamental)
What is the Timbre of sound?
It is used as pattern recognition to identify particular sound sources
It depends on the relative amplitude of components and discrete parts of the basilar membrane respond to each of the components, detecting their frequencies and amplitudes
What is sound intensity?
It is what we perceive as loudness and is determined by how each auditory
If a sound is intense, then each fibre attached will fire as hard as they can
If the sound is soft, it will fire randomly
What is loudness affected by?
Frequency
What is intensity cue?
Difference in timbre based on location and it is helped by the shape of pinna and outer ears
How is the location of sound inferred?
It is inferred based on the frequency and timing information of the sound
What are the 3 ways we use our ears to locate sound?
1) Pinnae - the shape determines how sounds are transmitted into the ear canal in a way that allows us to find the elevation of a sound source
2) The brain uses timing to determine where the sound comes from
3) Intensity - Head “shadows” sound so they are more intense at the close ear than the far one
Timing and cues are used by different structures early in the auditory neural pathway in the brainstem to determine sound locations
Where would humans be most sensitive to change in sound location?
In the midline but our ability to determine the location of objects through hearing is worse than our ability through touch or vision
What is motion parallax?
The idea that we perceive the world in 3D through a variety of cues
What are the two cues for 3D perception?
monocular depth cues are cues to distance that only depends on one eye
Relative motion is a cue to depth perception
What are binocular cues?
Cues to distance that depends on input from both eyes
What is retina disparity?
Degree to which light from an object falls on a different location on your left retina compared to your right
How does the one have visual perception?
The visual processing system takes visual sensations and turn them into perceptions
What prevents people from recognizing faces?
Lesions in the temporal cortex
Which part of the brain is responsible for facial recognition?
the fusiform face area, occipital face area and the posterior superior temporal sulcus and the amygdala
Is it easier to learn faces of people within our group or outside?
People within our group
Is it possible to improve facial recognition?
Yes through practice
What are the two interconnected streams of visual processing?
Ventral Stream and Dorsal Stream, and they must work together to produce useful and adaptive behaviour
What is the ventral stream?
It involves the bottom of the temporal lobe and allows us to see form, colour and motion. It also allows us to identify objects and attach meaning and significance to them.
What is the dorsal stream?
It involves the parietal cortex and allows us to perceive the location of objects so we can direct appropriate action to them
What is visual agnosia?
It is the inability for a person to recognize a familiar object through sight and is caused by damage to the ventral pathway
What is prosopagnosia?
Inability to recognize familiar faces
What is akinotopsia
The ability to recognize objects visually but not their movements
What is Neglect?
Inability to attend one side (usually the left) of the visual field or of an object and is caused by damage to the dorsal visual pathway
What is lateral inhibition?
When one receptor gets excited, it inhibits its neighbour, this mutual inhibition of neighbouring units is called lateral inhibition which results in perceiving lines when they do not exist
Why is lateral inhibition important?
Important as edges are important for decoding what objects are present in the environment
What are receptive fields?
- Receptors are wired together onto ganglion cells in a certain way
- A flash of light onto one part of a ganglion cell would cause excitement while another would cause it to become inhibited even though the light has no influence
- The area in which light onset or offset causes a change in the activity of a cell is called the receptive field
- The receptive fields of various ganglion cells overlap and together create visual space
- These cells have a doughnut-shaped ‘on centre, off surround’ receptive field
What is neural convergence?
- Signals from different neurons come together and meet at a single neuron which can add up the signals or compare them
- Neural convergence from retina to thalamus to cortex results in the formation of cortical neurons’ receptive fields
- Receptive fields in the retina and thalamus are circular but those in the cortex that are built up are bar shaped
o Sensitive to lines of different widths and to edges
o Specific for particular orientations relative to the orientation of the eye
o Some respond best to vertical bars, others to horizontal bars and some to oblique - Many of these neurons are orientation selective meaning they only respond when bars of light hit them at certain angles
How do the images arrive to our brain?
They arrive inverted and flat, so the brain has to infer a third dimension
What do images go through before reaching the photoreceptors?
many cell layers
Are there blind spots in our eyes?
yes
What is size constancy?
Mechanism that maintains the perception of a particular object as being of one size, in spite of the fact that the size of the image on the retina varies
What is perceptual constancy?
Mechanism that maintains a perceptual judgement as the external stimulus changes
What is lightness constancy?
Refers to the fact that the brain will perceive a surface as equally light regardless of illumination
What is form constancy?
The ability to recognize that an object is the same even if it is a different size
What is the phenomenon “form from motion”?
The phenomenon where movement can help perceive 3D forms
What is the structuralist approach to perception?
It argues that sensations are building blocks to perceptions and by understanding sensations, one can understand perceptions
Is the structuralist approach true?
No it is not true because vision is more than elemental sensations chained together
What is the Gestalt approach?
It argues that perception is more than a sum of sensations, rather we have predispositions to perceive things in set ways. Incoming sense data is organized in such a way that we perceive whole objects.
What is the constructivist approach?
We actively interpret incoming sense data, rather than passively receive it and prior knowledge important in guiding perception
What is a concave surface?
Objects are shaded near their tops and bright at their bottoms
What is a convex surface?
Objects are shaded near their bottom and bright at their top
Where are humans accustomed to light coming from?
above their heads
Is the perceptual system foolproof?
No but it uses multiple cues
How does the visual system arrive at a close interpretation?
it weighs and combines guesses based on experience
What are feature detectors?
Cells are sensitive to stimulus features; cells become sensitive to complex feature of stimulus
What are ganglion cell receptive fields?
The receptive field of a cell is the area on the retina over which the behaviour of that cell can be directly influenced
What is the ecological (functionalist) approach?
Perception is explained in relationship to the properties of the world around us. It argues surface and their textures are important. Our detection of movement and change within our visual field also provides crucial information. Our visual system has evolved to only detect what is important.
What is the optic flow?
the concept that as we move around the world, the world flows by us and we use that information to tell us how far things are away from us and about our motion
What is the law of Pragnanz?
It argues that our perceptual world is organized into the simplest pattern that is consistent with the sensory information and with our experience
What are some strengths of the Gestalt account?
It recognizes some limitations of structuralist views and the principles of perceptual organization recognized is still current.
