VISUAL - sensation and preception

Sensation vs. Perception

sensation: is the process of detecting unprocessed sensory information from the environment

perception: is the brains process of organizing and interpreting sensory information, giving it meaning.

• sensation = input of raw data, perception = interpretation of data

What’s stimuli?

an energy in the environment that can be detected by your senses

What is transduction?

process where sensory organs convert physical/chemical stimuli from the environment into electrical signals that the brain understand

• Vision: Light hitting the retina → converted into neural signals.

  • Without transduction, your brain couldn’t interpret any sensations—it’s the “translator” between the outside world and your brain.

brain interprets these as sight, smell, touch, taste, and hearing

What are the sensory receptors?

Specialized cells that detect specific types of stimuli from the environment and starts the process of transduction (converting into neural signals)

How are sensory receptors connected to the brain?

connected to the brain via neurons, which transmit the neural signals during transduction'

what are afferent neurons?

sensory neurons that carry neural signals from sensory receptors toward the central nervous system (brain and spinal cord)

• messengers between sensory receptors and the brain. Without them, transduction wouldn’t reach the CNS, and you wouldn’t perceive the sensation.

What are thresholds

How we categorize the level of degrees in which our sensory systems detect energy (stimuli). It helps categorize how sensitive our senses are to detecting or noticing changes in stimulation.

What is the absolute threshold

It’s the lowest level of stimulation we can detect at least 50% of the time by our senses. 

• you’re not always aware of it because its right on the edge of your ability to sense it. (sometimes you notice it sometimes you don’t)

  • like a border: one side the stimulus is too weak to detect, above it you can detect it clearly

What is the difference threshold AKA Just noticeable difference (JND)?

the smallest change between two stimuli that can be detected 50% of the time

• how much something has to change before you notice it

What’s Webers Law?

To notice a difference between two things, the change has to be big enough in proportion to how strong the original thing is

• the bigger or louder something is, the more it has to change before you can tell the difference

  • You can tell the difference if you add 1 gram to a 10-gram weight.

  • But if you’re holding 100 grams, you won’t notice 1 more gram — you’d need around 10 grams extra to feel the change.

What is the subliminal threshold?

level of stimulus that is too weak to be consciously detected, but may still influence your thoughts or behaviour

• don’t consciously notice, but brain still sometimes registers

  • ex: smell of food that you unconsciously smell and then as a result you become hungry

What’s subliminal perception?

the actual process of the brain registering the weak stimulus that isn’t detected consciously which as a result, influenced your behaviour

What’s subliminal adaptation

when stimuli is so weak and overtime your brain adjusts becoming even less likely to respond to it

• A very faint background smell in a room that you don’t notice, and after being in the room for a while, your brain completely ignores it.

What’s bottom-up vs Top-down processing?

• bottom up processing (baby)

  • begins with raw sensory input from the environment in which the brain builds a perception on

  • think baby because they have little prior knowledge/experience so they rely heavily on the input to make sense of the world

• Top-down processing (adult)

  • begins with prior knowledge, experiences, expectations, or context so your brain interprets sensory info based on what it already knows

  • Starts with perception → interpreting sensory data

  • think adult because Adults have more knowledge, experience, and expectations, so they can interpret sensory information faster and more efficiently.

What’s signal detection theory (SDT) ?

Shows how we detect signals in noisy situations, based on both sensory ability and judgment.

• Detection is not just about the strength of the stimulus — it’s also influenced by attention, expectations, motivation, and experience.

What are the four possible outcomes in SDT?

1. hit: correctly detecting a signal when its present

2. Miss: failing to detect that signal when its present

3. False alarm: reporting a signal when none is present

4. Correct rejection: correctly identifying that no signal is present

What is light?

Form of electromagnetic energy that can be detected by rods and cones and described in terms of intensity (brightness) and wavelengths (colour).

What’s a wavelength?

determine the colour of light that we perceive 

• a short wavelength is blue/violet (think calm)

• medium wavelength is green (think neutral)

• Long wavelength is red (think big and powerful)

What are the three visible parts of the eye and what do they do?

• sclera

  • White outer part that protects eye and maintains the shape

• Iris

  • Coloured part that contains muscles that control the pupil and regulates how much light enters

• Pupil

  • lets the light in which is controlled by iris

    

What are the other parts of the eye (5)?

• Cornea: clear membrane

  • bends light to help focus it on retina

• Lens: transparent and flexible structure

  • changes shape to focus light on the retina (think camera lens)

• Retina:

  • inner layer at back of eye that includes photoreceptors (rods and cones)

• Fovea

  • small pit in retina which has the sharpest video and highest concentration of cones

• Optic nerve

  • carries info from retina to brain

What are Rods?

photoreceptor cells I the retina that detect low light levels and help with night vision

• highly sensitive to light, but cannot detect colours

• more numerous than cones

What are cones?

photoreceptor cells in the retina that detect colour and fine detail

• works best in bright light

• responsible for colour vision (red, green, blue)

• concentrated mostly in fovea

What is a blind spot?

where the optic nerve leaves eye and there are no photoreceptors

How does the brain process visual information?

1. once the photoreceptors detect the light it gets converted into electrical signals (transduction)

2. then those travel through the optic nerve (made up of afferent neurons) and reach the brain

3. then visual info reaches the occipital lobe (visual cortex)

• which processes colour, shape, motion, and depth

4. perception is created (becomes aware of what you see)

What does the visual cortex do?

Located in occipital lobe where it interprets colour, shape, motion, and depth.

• combines info from both eyes to create a coherent visual perception

  • main hub where brain interprets those signals

How does visual information get processed so fast?

Parallel processing.

What is parallel processing

brains ability to simultaneously process multiple types of sensory info

• instead of handling one feature at a time the brain processes colours, shape, motion, depth, etc, all at once

What is depth perception 

the brains ability to judge how far away objects are and perceive the world In three dimensions (3D).

• allows us to navigate our environment and interact with object

• uses binocular clues and monocular cues

Binocular depth cues vs. monocular depth cues

binocular depth cues - require both eyes

• help judge distance and depth for close objects

  • fine-tuned depth

Monocular depth cues - only one eye

• helps judge distance and depth for far objects

  • general depth

What are two examples of binocular depth cues?

• retinal disparity; each eye sees slightly different images, the brain combines these to judge distance

• convergence: Eyes angle inward more when looking at something close; less when looking far

What are 7 examples of monocular depth cues?

• height in the field

  • higher = farther, and lower = closer

• Familiar size

  • judge distance based on how big we know an object should be

• Linear perspective

  • parrelel line appear to meet in the distance'

• overlap

  • objects blocking others are closer

• shading 

  • light & shadows make objects look 3D

• Clarity 

  • far objects look faint/blurry

• Texture gradient

  • texture decreases the further it gets

What are the two theories of colour perception?

Trichromatic colour theory and opponent-process colour theory

what is the opponent-process colour theory?

theory suggests that colour vision is based on opposing pairs of colours rather than individual colour receptors

• visual system interprets colours using antagonistic channels, meaning activation of one colour in a pair inhibits the other

  • ex: Red ↔ Green, Blue ↔ Yellow, Black ↔ White

• why this happens: ganglion neurons which are In the retina are opponent cells meaning they react differently ti two opposing colours

  • excited by one (cells fire more), inhibited by the other (cells fire less)

What is the Trichromatic colour theory?

theory based on how we see colour based on three types of cones in the retina

• Red-sensitive cones → respond to long wavelengths

• Green-sensitive cones → respond to medium wavelengths

• Blue-sensitive cones → respond to short wavelengths

colour is perceived by combining those wavelength levels of the three cone types

What is perceptual consistency?

brains ability to perceive objects as stable and unchanging

• size consistency: objects appear the same size even if they are closer or farther away

• shape consistency: objects maintain their shape even when the angle of the view changes

• colour consistency: objects maintain their colour even under different lighting

What are feature detectors?

specialized neurons in the visual cortex that respond to specific features a visual stimulus.

• edges and lines

• movement

• angles and shapes

what is Perceiving forms?

brains ability to organize visual info into recognizable shapes and objects

• figure ground: separating an object from its background

• closure: filling in missing info to perceive a complete shape

• proximity and similarity: grouping elements that are close together or similar in appearance