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Samenvatting Sensation and Perception Deel 2

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Universiteit Utrecht (UU)

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Sensation

Dit is de samenvatting voor het tweede deel van de cursus Sensation and Perception, gegeven aan de Universiteit Utrecht. Het omvat de volgende onderwerpen: Motion, The Vestibular System and the Ear, Higher audition, Touch, Smell en Taste. In deze samenvatting vind je een complete samenvatting van ...

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Sensation and Perception
Part 2

Inhoudsopgave
Chapter 8 – Motion...............................................................................................................................................1
Chapter 9 – Hearing..............................................................................................................................................4
Chapter 12 – Vestibular system..........................................................................................................................11
Chapter 10 – Hearing in the Environment..........................................................................................................15
Chapter 9 – Music and Speech Perception.........................................................................................................19
Chapter 13 – Touch.............................................................................................................................................20
Chapter 14 – Olfaction........................................................................................................................................25
Chapter 15 – Taste..............................................................................................................................................30
Lecture 8 – Motion..............................................................................................................................................34
Lecture 9 – The Vestibular System and the Ear..................................................................................................38
Lecture 10 – Higher audition..............................................................................................................................47
Lecture 11 – Touch..............................................................................................................................................53
Lecture 12 – Smell...............................................................................................................................................60
Lecture 13 – Taste...............................................................................................................................................67
Paper 21 – Relearning sound localization with new ears...................................................................................74
Paper 25 – Tactile acuity is enhanced in Blindness............................................................................................74
Paper 29 – Olfaction Modulates Visual Perception in Binocular Rivalry............................................................75
Paper 30 – Intense Sweetness Surpasses Cocaine Reward................................................................................76

Chapter 8 – Motion

Motion can be seen as a low-level perceptual phenomenon as is seen with cells in our cortex
that respond to motion in one particular direction. After viewing motion in a constant
direction for a sustained period of time (at least 15 seconds or so) we see any stationary
object that we view subsequently as moving in the opposite direction; motion aftereffect.
Just as color aftereffects are caused by opponent processes for color vision, MAE is caused
by opponent processes for motion detection.
Neurons tuned to different directions of motion generally do not respond to a stationary
object, so they simply continue to fire at their spontaneous rate; and the spontaneous rate
for upward and downward are normally balanced. However, when we observe motion in a
particular direction for a sustained period, the detectors to that motion become adapted
and the not adaptive neurons fire faster and therefore we perceive something stationary as
it is moving in the opposite direction.

These MAE’s are still present when one eye is adapted, and you look with the other; this
means this effect must be reflecting the activities of neurons in a part of the visual system

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,where information of both eyes is combined. For motion, this brain area is the middle
temporal cortex, referred to as MT or V5 in humans.

The bilocal correlator (Reichardt detector): based on a physiological measurement of the
difference between point A and point B and you look at span and delay, which is basically
the same as space and time. In physiological systems, all come down to variations on the
bilocal correlator theme. This is also called Reichardt detector.

One possible objection to the Reichardt model is that it does not require continuous motion
in order to fire. An image that appears, then disappears and then reappears in a latter
receptive field in a short window will drive cells to respond just as strongly as if the image
has moved. This is what is called apparent motion: the illusory impression of smooth motion
resulting from the rapid alternation of objects.
The aperture problem: the fact that when a moving object is viewed through an aperture (or
receptive field), the direction of motion of a local feature or part of the object may be
ambiguous. It is an example of a correspondence problem: problems faced by the motion
detection system of knowing which feature in Frame 2 corresponds to which feature in
Frame 1. The aperture is in this case the opening that allows only a particular view of that
object. Remember that every V1 cell sees the world through a small aperture. Thus, none of
the V1 cells can with certainty tell which visual elements correspond to another when an
object is moving. The correct observation comes when these responses are combined.

Detection of global motion is done by the magnocellular layers in the LGN, which project to
the V1 and then go on to the MT. The vast majority of cells in the MT are direction specific
and show little sensitivity for form and color. Information that the MT is indeed critically
involved in processing global motion comes from (leasion) studies in monkeys where they
first trained monkeys to detect correlated dot motion. Were able to do this when 2-3% of
the dots were moving in that direction, after lesion only when 20-30% of the dots were
moving.

First order motion: the change in position of luminance-defined objects (object that is
delineated by differences in reflected light) over time.
Second-order motion: the motion of an object that is defined by changes in contrast or
texture but not by luminance. Here we look at texture and contrast defined objects (and
thus not defined by luminance) The fact that almost all humans (and other animals) can
perceive second-order motion is a strong indicator that the visual system does not simply
track objects’ positions over time to calculate movement.
As you can see, every white pixel in Image 2 has been changed to black in Image 3, and vice
versa. The only thing that changed in Image 1 was the color of the pixels—nothing in this
image is actually moving at all: nothing actually moves in second-order motion.

There have been double dissociations where people still have first order motion but not
second order motion and vice versa. The motion aftereffect is also more abundant in second
order motion then in first order motion.

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,Motion Induced Blindness (MIB) is a phenomenon of visual disappearance or perceptual
illusions observed in the lab, in which stationary visual stimuli disappear as if erased in front
of an observer's eyes when masked with a moving background.

Optic flow: the changing angular positions of points in a
perspective image that we experience as we move through
the world. The optic array is then the collection of light rays
that interact with objects in the world that are in front of the
viewer. The focus of expansion is the point in the center of
the horizon from which, when we are in motion, all points in
the perspective seems to emerge (red dot).
Lack of optic flow is a signal that you are stationary. This also
explains the illusion of motion when a neighboring train
passes by.

Biological motion: the pattern of movement in living (human) beings. Thus, motion can help
us inform about the nature of objects. Biological motion appears to play an important role in
how we interpret human actions (e.g. fighting or dancing).

Our eyes are constantly moving but we know really good which motions on the retina belong
to real movements and which are caused by our own eye and head movement.
Smooth pursuit: a type of voluntary eye movement in which the eyes move smoothly to
follow a moving object.
The superior colliculus is a structure in the midbrain that is important in initiating and
guiding eye movements. If a cell in the superior colliculus is activated, the eye moves toward
that specific location. The SC also gets information directly from retinal ganglion cells which
helps with planning of eye movements. Even when we hold our eyes stationary they will
continue to make micro saccades important since otherwise stationary targets will fade from
view. Micro saccades also seem important for very fine spatial judgement, compensating for
the very rapid falloff of acuity even a few minutes outside the fovea.

Three types of voluntary eye movements:
 Smooth pursuits
 Vergence eye movements when we rotate our eyes inwards or outwards
 Saccade: a fast jump of the eye that shifts our gaze from one spot to another.
Involuntary eye movements:
 Vestibular eye movements: when the eyes move to compensate for head and body
movement while maintaining fixation on a particular target.
 Optokinetic nystagmus (OKN): reflexive eye movement in which the eyes will
involuntarily track a continually moving object.

Saccadic suppression: when we make a saccade, the visual system essentially shuts down for
the duration of the eye movement; mainly to suppress information carried by the
magnocellular pathway. Thus, you can’t see your eyes moving in the mirror.

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, By sending two copies of each order to
move the eyes, the motor system is
thought to solve the problem of why
an object moving across the retina may
appear stationary. One copy goes to
the eye muscles, another (the
efference copy) goes to an area of the
visual system that has been dubbed
the comparator. The comparator can
compensate for the image changes
caused by the eye movement,
inhibiting any attempts by other parts
of the visual system to interpret the
changes as object movement. If we
juggle the eyeball with a finger, no signal is sent to the eye muscles to the comparator (since
the eye muscles do not move the eyeball in this case) the visual input is interpreted as our
world being rocked.

Chapter 9 – Hearing

Sound: created when objects vibrate: the vibrations of an object cause molecules in the
surrounding medium to vibrate as well. The speed of sound is about 340 meters per second,
under water this is about 1500 meters per second.
The magnitude of pressure changes in a sound wave – the difference between the highest
pressure and the lowest pressure of the wave is called the amplitude (or intensity). Rate of
this fluctuation (in light called wavelengths) are in sound described as the frequency of the
wave. Sound waves are measured with the unit Hertz (Hz) where 1 cycle per second equals 1
Hz.
Amplitude is associated with the perceptual quality of loudness: the more intense a sound
wave is, the louder it will sound.
Frequency is associated with pitch: low-frequency sounds correspond to low pitches (e.g.
notes: toonhoogtes).

Human hearing is limited to a range of frequencies that varies from 20-20.000 Hz. Also,
humans hear across a very wide range of sound intensities. To describe differences in

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