Sensation and perception
- Sensation is detecting stimuli with the senses, such as light reaching the eyes.
- Perception is processing and interpreting that information to make sense of it, such as recognising a face.
Depth cues
- Monocular depth cues work with one eye: height in the visual field (further objects appear higher up), relative size (smaller objects seem further away), occlusion (nearer objects cover further ones), and linear perspective (parallel lines seem to meet in the distance).
- Binocular depth cues need both eyes: retinal disparity (each eye sees a slightly different image) and convergence (the eyes turn inwards more for close objects).
Visual illusions
- Ambiguity: an image can be seen in two ways, such as the Necker cube or Rubin's vase (a vase or two faces).
- Misinterpreted depth cues: the Ponzo illusion and the Müller-Lyer illusion make lines of equal length look different.
- Fiction: the brain sees something that isn't there, such as the Kanizsa triangle.
- Size constancy: we know objects stay the same size even as they get further away, which illusions like the Ames room can trick.
Key terms
- Sensation
- Detecting stimuli with the senses.
- Perception
- Processing and interpreting sensory information.
- Monocular depth cue
- A depth cue that works with one eye.
- Binocular depth cue
- A depth cue that needs both eyes.
- Occlusion
- A nearer object covering part of a further one.
- Retinal disparity
- Each eye seeing a slightly different image.
- Visual illusion
- An image that tricks the brain into perceiving something wrongly.
- Size constancy
- Knowing an object's size stays the same as its distance changes.
Practise Sensation, perception and visual illusions: 10 questions