C5: Sensation and Perception

Translation of stimuli into neural impulses - these impulses first travel to the thalamus, then onto different cortices

Decreasing responsiveness to stimuli due to constant stimulation

Our perception of sensations is partially due to how focused we are on them

The ability to focus one’s attention on a particular stimulus while filtering out a range of other stimuli.

1. Reflected light first enters the cornea that focuses the light

2. Light goes through the pupil

3. Accommodation (light that enters the pupil is focused by the lens. as light passes through the lens, the image is inverted)

4. The focused inverted image projects on the retina which has specialized neurons that are activated by the different wavelengths of light

Activated by colour (concentrated towards the centre of the retina)

Respond to black and white (outnumber cones and are distributed throughout the retina)

An indentation at the centre of the retina that contains the highest concentration of cones

If enough bipolar cells fire, the next layer, ganglion cells, are activated.

• The axons of the ganglion cells make up the optic nerve that sends these impulses to the lateral geniculate nucleus (LGN), which is an area in the thalamus

The spot where the optic nerve leaves the retina and has no rods or cones

Spot where the nerves cross each other

Discovered that groups of neurons in the visual cortex respond to different types of visual images (feature detectors for vertical lines, curves, motion, etc.)

3 types of cones in the retina: cones that detect blue, red, and green

• Cones are acitvated in different combinations to produce all the colours of the visible spectrum

  • Cannot explain some visual phenomena

Sensory receptors arranged in the retina come in pairs (red/green, blue/yellow, black/white)

• If one sensor is stimulated, its pair is inhibited from firing

  • Can explain visual phenomena

• If you stare at one colour for a while and then look at a white or black space, you will see a colour afterimage

  • If you stare at green, the afterimage is red. For blue, it is yellow.

Dichromatic: cannot see either red/green or blue/yellow shades

Monochromatic: can only see shades of grey

The eardrum connects with the hammer (malleus), which connects to the anvil (incus), which connects to the stirrup (stapes)

Sound waves are collected in your outer ear and travel down the ear canal until they reach the eardrum (tympanic membrane)

• The membrane vibrates as the sound waves hit it and is attached to the first in a series of ossicles

• The vibration of the eardrum is transmitted by the ossicles to the oval window which is attached to the cochlea (a structure shaped like a snail’s shell filled with fluid). As the oval window vibrates, the fluid moves.

  • The floor of the cochlea is the basilar membrane. It is lined with hair cells connected to the organ of Corti, which are neurons activated by movement of the hair cells. When the fluid moves, the hair cells move and transduction occurs. The organ of Corti fires, and these impulses are transmitted to the brain via the auditory nerve.

Hair cells in the cochlea respond to different frequencies of sound based on where they are located in the cochlea

• Some bend in response to high pitches and some to low

• We sense pitch because the hair cells move in different places in the cochlea

• Place theory accurately describes how hair cells sense the upper range of pitches, but not the lower tones.

• Lower tones are sensed by the rate at which the cells fire

  • We sense pitch because the hair cells fire at different rates (frequencies) in the cochlea

Occurs when something goes wrong with the system of conducting the sound to the cochlea (in the ear canal, eardrum, hammer/anvil/stirrup, or oval window)

Occurs when the hairs in the cochlea are damaged, usually by loud noise

• Prolonged exposure to loud noise can permanently damage the hair cells in your cochlea, and these hair cells do not regenerate

• Some pain messages have a higher priority than others

• When a higher priority message is sent, the gate swings open for it and swings shut for a low priority message, which we will not feel

• Endorphins (pain-killing chemicals) also swing the gate shut

Tells us how our body is oriented in space

• 3 semicircular canals filled with fluid in the inner ear give the brain feedback about body orientation

• Tells us about the position and orientation of specific body parts

• Receptors in our muscles and joints send info to our brain about our limbs

  • This info, along with visual feedback, lets us keep track of our body

The smallest amount of stimulus we can detect

Used to describe stimuli below our absolute threshold

The smallest amount of change needed in a stimulus before we detect a change.

Computes the just-noticeable difference threshold

• States that the change needed is proportional to the original intensity of the stimulus. The more intense the stimulus, the more it will need to change before we notice a difference

  • Each sense varies according to a constant, but the constants differ between the senses

Investigates the effects of the distractions and interference we experience while perceiving the world.

• Tries to predict what we will perceive among the competing stimuli (takes into account how motivated we are to detect certain stimuli and what we expect to perceive)

• All the above factors are called the response criteria

• False positive (when we think we perceive a stimulus that is not there)

• False negative (when we don’t perceive a stimulus that is present)

We perceive by filling in gaps in what we sense. It occurs when you use your background knowledge to fill in gaps in what you perceive.

Mental representations of how we expect the world to be based on our experience.

Predisposition to perceiving something in a certain way (e.g. backmasking)

• We use only the features of the object itself to build a complete perception

• Feature detectors in the visual cortex allows us to perceive basic features, such as lines, curves, motions, etc

• Our mind builds the picture from the bottom up using these basic characteristics

Images in a series of still pictures presented at a certain speed will appear to be moving.

A series of lightbulbs turned on and off at a particular rate will appear to be one moving light.

If a spot of light is projected steadily onto the same place on a wall of an otherwise dark room and people are asked to stare at it, they will report seeing it move.

Used the visual cliff experiment to determine when human infants can perceive depth