LO7 - Sensation and Perception 1

Question 1

Sensation

Answer 1

The ability to detect a stimulus. Features of the environment that are used to create understanding of the world.

It is external energy

Question 2

Perception

Answer 2

The act of giving meaning to a detected stimulus. Combining of sensations arriving from the sensory system with prior knowledge.

It involves understanding what a stimulus is.

Question 3

Transduction

Answer 3

Conversion of one energy to another. It is a process where a stimuli such as light energy is converted into neural electrochemical energy.

Question 4

Psychophysics

Answer 4

The science of defining quantitative relationships between the physical and psychological events.

It is research aimed at relating physical stimuli to the contents of consciousness such as sensations.

It was developed by Fechner who lost his sight from looking at the sun too much which led him to become interested in the connection between physical stimuli and conscious perception.

Question 5

Absolute threshold

Answer 5

The level of stimulus intensity required to create a conscious experience. This varies between individuals.

Question 6

Signal detection theory

Answer 6

This accounts for individual biases and was developed to account for variability.

Experiments take into account false alarms as well as detection. Misses are when a stimulus was there but not detected, false alarms are where there was no stimulus but some stimulus was thought to be detected.

Question 7

Just noticeable difference

Answer 7

The smallest magnitude of stimulus requires to detect discrete stimuli (advanced in Weber’s law)

Our sensations are on a spectrum. At what point can we decide that they are separate entities?

Question 8

Perception: how do we assign meaning to incoming sensory information?

Answer 8

We can use either bottom-up or top-down processing.

Question 9

Bottom-up processing

Answer 9

Processing the elementary messages from the environment.

A meaningful signal is created starting from the sensory input.

It is data-driven and processes raw data. It assumes that we are unbiased without prior beliefs.

Question 10

Top-down processing

Answer 10

Applying memory, knowledge etc to understand and create a perception.

Perceptions are form from a larger concept idea - we work first from the general to the details

Our abstract impressions influence the information that we gather through our senses.

We have a template that we apply sensory information to and look for reaffirmation of this template.

Question 11

Vision detection origins (expromission theory of vision)

Answer 11

We see through vision beams coming out of our eyes and latching on to objects.

Plato first proposed this and Galen supported it.

This idea is still prevalent in our thinking about vision (in 2002, 50% of American adults believed in this).

Question 12

Intromission theory of vision

Answer 12

This has replaced expromission theory of vision and it is the opposite.

Visual perception comes from some representation of the object entering the eyes.

It is light energy (electromagnetic) that enters our eyes.

Question 13

Light energy (vision)

Answer 13

Light can be thought of as a wave (stream of photons). This is electromagnetic energy but we only detect a small band between 400-700nm.

Wavelength determines the perceived hue/colour. It is the length from one peak to another and is determined by frequency which controls the cycle rate.

Amplitude determines the brightness/intensity and this is the height of the wave.

Question 14

The Eye - The Cornea

Answer 14

Transparent tissue which allows light rays to enter the eye and focus on objects.

It bends light and focuses it onto the retina.

Question 15

The Eye - The Iris/Pupil

Answer 15

This is the coloured part of the eye and it consists of muscular diaphragm which regulates the light entering the eye by expanding and contracting the pupil.

It regulates the size of the pupil to regulate how much light enters.

Question 16

The Eye - The Lens

Answer 16

This is the crystalline lens inside the eye that enables the changing of focus.

It is attached to supplementary ligaments that allow it to contract and relax. The change in shape allows focus to change, this is called accommodation.

Question 17

The Eye - The Retina

Answer 17

This contains photoreceptors (light-sensitive neurones). From here, light gets transducer into a neural signal.

It is at the back of the eye and is a light-sensitive membrane.

The design is specialised in its circuitry to collect light information in a certain way.

Question 18

The Eye - The Fovea

Answer 18

This is a point within the retina. Small pit that contains the highest concentration of colour sensitive light receptors.

It has the highest visual acuity in the retina.

Question 19

The retina (cross section)

Answer 19

We see three layers of cells:

1. Photoreceptors
2. Bipolar cells
3. Ganglion cells

Ganglion cells send action potentials via the optic nerve into your brain.

Light sensitive cells are found at the back of the eye perhaps for protection or light filtering.

Question 20

Photoreceptors

Answer 20

These transducer light into neural activity.

There are two kinds: rods and cones.

Question 21

Rods

Answer 21

These are adapted for dim light. They are sensitive to all wavelengths of light.

They are used for black and white vision and form a low resolution image.

This means there is one bipolar cell to many rods. There are around 100 million in each human eye (most common).

They are promiscuous as they try to gather as much information as possible.

Question 22

Cones

Answer 22

These function to perceive bright light and work most in daytime.

They are sensitive to blue/red/green wavelengths of light and provide us with colour vision.

They are high resolution as there is one bipolar cell to one cone.

We have around 5 million cones in each human eye. A smaller proportion of the retina is made up with cones.

Question 23

Photoreceptors - location in the retina

Answer 23

Rods are found on the periphery and respond to the amount of light. They signal information about motion.

Cones are found in the fovea (centre). They respond to the quality of light and send information about detail.

Fovea is associated with clarity of vision. That’s why there are so many cones in that one place.

Question 24

The Eye - Blindspot

Answer 24

This is where the optic nerve leaves the eye and there are no photoreceptors.

This exists because where there are capillaries and the optic nerve, there cannot be photoreceptors.

The visual system fills the blindspot with information from the surrounding area and makes predictions.

Question 25

Colour detection - perception of wavelength

Answer 25

There are three subtypes of cone:

1. S-cones are short wavelength cones and pick up blues
2. M-cones are medium wavelength cones and detect yellows and greens
3. L-cones are long wavelength cones and detect reds.

We don’t call the types of cones by their colour because this is not a physical property of the world, it is a result of the interaction between an electromagnetic wave and a nervous system.

Question 26

Trichromatic

Answer 26

We are trichromats because we have three types of cone and detect difference in colour based off this.

We see a full spectrum from different activations.

Hummingbirds are tertachromats because they also see UV rays and have 4 types of cones.

They have an additional level of perception.

Question 27

Bipolar cells.

Answer 27

These are intermediate cells that determine the information from photoreceptors to ganglion cells.

There are two general classes: diffuse and midget.

Question 28

Diffuse bipolar cells

Answer 28

These are found in the periphery.

They each respond to around 50 rods which means they have increased sensitivity but reduced acuity.

There is a convergence of information as many rods pass information to once diffuse bipolar cell.

They require input from three photoreceptors to send action potentials to its ganglion cell. They fire a lot as there are 50 so there is a high chance at least 3 will get hit.

We cannot tell which 3 got hit - pooling of information

Question 29

Midget bipolar cells

Answer 29

These are found in the fovea and receive input from a single cone and pass on information to a single ganglion cell.

They have a higher amount of visual acuity as they know exactly which cone fired. A high quantity of accurate information is passed on.

Question 30

Ganglion cells

Answer 30

These are the final layer of cells and are the output (final stage of processing before info is sent out of the optic fibre).

There is over 1m kinds of ganglion cell.

Diffuse bipolar cells synapse onto M cell (periphery)
Midget bipolar cells synapse onto P cell (fovea and clarity)

Question 31

Optic fibre

Answer 31

This connects to the brain.

Axons of the ganglion cells project out of the fibre.

Question 32

Retinal ganglion cells

Answer 32

These form the optic tract.

The receptive field is the region on the retina in which visual stimuli influences neural firing rate.

One ganglion cell responds to activity/light that falls on their specific cluster of photoreceptor cells.

Ganglion cells respond to presence/absence of light as well as patterns within their receptive field

Question 33

On-centre/Off-surround retinal ganglion cells

Answer 33

A ganglion cell that increases firing in response to increase in light intensity in its receptive field.

When light hits the centre - firing rate is at the maximum, when light covers full receptive field, firing rate returns to the baseline. When light is on surround, baseline firing is repressed.

There are pattens of light that cells fire most to

Question 34

Off-centre/On-surround cell

Answer 34

A ganglion cell that increases firing in response to decrease in light intensity in its receptive field.

Function is contrast in illumination to help detect object edges, where it is daytime or night, indoors/outdoors etc.

Question 35

Colour Detection - Opponent process theory

Answer 35

P-cells fire rapidly to one wavelength and reduce to another. This forms pairs of colours: Red-Green, Blue-Yellow, Black-White.

E.g. reduction of red firing = green.

This process is involved in retinal ganglion cells.

Question 36

Trichromatic theory

Answer 36

Colour vision occurs by comparing the activation of the three cones.

We see a full spectrum from different activations of these cones.

Question 37

The visual pathway

Answer 37

Information from the retina leave the eye via the optic nerve (ganglion axons).

Information from the optic nerve travels to the optic chasm (cross over occurs).

Lateral geniculate nucleus (LGN) of the thalamus is the sensory relay centre.

Then it goes to you visual cortex/V1

Visual information from the left side of both eyes is channelled to your right hemisphere and vice versa.

Question 38

Visual cortex - feature detectors

Answer 38

The visual cortex (V1) responds to different patterns of light at particular points in our visual field.

Individual neurones in the visual cortex show orientation selectivity. Visual cortex feature detectors are more tuned towards lines.

Huber and Wiesel found this in 1958.

Receptive fields of striate context are not circular but elongated.

Question 39

Simple Cells (feature detectors)

Answer 39

Neurones fire vigorously when the line is oriented vertically but reduces firing horizontally and vice versa.

Question 40

Complex cells (feature detectors)

Answer 40

Fire most when lines are in certain motion. E.g. they will fire most when a line moves from left to right.

They may hardly fire when a line moves from up to down.

Question 41

Visual cortex - there is more variation in V1 cell firing than retinal cells.

Answer 41

Spike trains show patterns of APs firing.

A neurone in VI (visual cortex) will leave almost three separate traces for the same stimuli.

A neurone in LGN (Right outside retinal output) acts like a camera and takes a snapshot of the same stimulus again and again. This causes similar traces to form.

VI shows us that we are not having the same perception of the same image each time as you notice new things each time.

Question 42

Visual cortical pathways

Answer 42

This is processing after the visual cortex. Information leaves the visual cortex in two ways:

1. The what stream is the ventral stream to the temporal lobe. This is about object recognition.
2. The where stream is the dorsal stream to the parietal lobe. This is about location of objects in space.

Question 43

Gestalt psychology

Answer 43

Gestalt is a psychological term referring to unified whole

It refers to theories of visual perception developed by the German psychologists in the 1920s.

Gestalt psychology describes how people tend to organise visual elements into whole entities.

Question 44

Gestalt principles

Answer 44

Gestalt psychologists believe we are born with specific predisposed ways of organising information that gives it utility.

Attempted to define universal rules about how the visual system organises data into unified wholes.

Top-down processes - predispositions that give information meaning.

Question 45

Figure-ground rule

Answer 45

The eye differentiates an object from its surrounding area.

A form, silhouette or shape is naturally perceived as figure (object), while the surrounding area is perceived as ground.

This links to retinal ganglion cells as it is ability to bring forward the object of interest and push the background back.

Question 46

Principle of proximity

Answer 46

Occurs when elements are places close together. They tend to be perceived as a group.

Question 47

Principle of similarity

Answer 47

occurs when objects look similar to one another. People often perceive them as a group or pattern

Question 48

Principle of closure

Answer 48

Occurs when an object is incomplete or a space is not completely enclosed. If enough of the shape is indicted, people perceive the whole by filling in the missing information.

Our minds close blanks.

Question 49

Principle of continuation

Answer 49

Occurs when the eye is compelled to move through one object and continue to another object.

Question 50

Principle of common fate

Answer 50

Occurs when objects that are moving together will be grouped together.

Question 51

Biological motion

Answer 51

The pattern of movement of living beings (human and animal).

We use motion to identify the nature of objects/beings. This helps us to identify specific people and human intent.

When shown 13 dots moving we will see a walking pattern.

We can identify a lot of information from not much stimuli.

Question 52

Blindsight

Answer 52

Damage/lesions in the visual cortex can lead to conscious blindness.

This typically only occurs on one side - blindness is in the opposite visual field making you half blind.

Other lower pathways/LGN are intact.

If you present an image to their blind visual side, they will say they are blind but when they are told to guess, they get it right above chance. They can identify object shape, localise objects and detect emotions.

Question 53

Blindsight explanation

Answer 53

Suggests that some information is still being transmitted from the eyes to the lower visual processing which is guiding out behaviour.

We have both conscious vision (we know what we see) and unconscious vision (decisions can occur outside our awareness)

Some sort of signal is being detected.

Question 54

Impaired recognition - visual agnosia

Answer 54

This is the inability to recognise visual objects. We can see colour, shape and faces but can’t assign meaning to them.

This can arise from strokes or brain trauma and is caused by damage to the ventral/dorsal visual pathways.

Question 55

Impaired recognition - prosopagnosia

Answer 55

This is the inability to recognise faces. Patients show emotional responses to very close relatives which suggests that unconscious emotional recognition is taking place when conscious recognition is not.

The visual stimulus of a face cannot be put into a full perceptual meaning.

This is associated with issues in your ventral pathway (what).

Question 56

Impaired recognition - Akinetopia

Answer 56

This is the inability to detect motion and patients see life in a series of snapshots.

Biological motion is impaired and there is difficulty in detecting people from their gates.

The ability to assign meaning is impaired.

Question 57

Sensory substitution

Answer 57

‘Brainport’ can help blind people to see using electrical impulses on the tongue which draws an image for the person.

It retrains how the brain processes information and they learn to interpret touch as sight in the visual cortex.

The patient can spot objects and navigate an obstacle course.

Tactile stimulation can be translated into information that the visual cortex can use.

Question 58

Sensory substitution - we see with our brains not our eyes

Answer 58

It is the visual cortex that provides the understanding of what we see.

Our brains are highly plastic and blind patients can use tactile sensation from the tongue and translate this into a visual perception.

This suggests a hardwired perception of the world. We have a base template of the visual world and the best information to fill this template is visual but when this is not available, we can use tactile information