What is the fundamental difference between monocular and binocular depth cues?

Monocular cues can be perceived with only one eye and often rely on environmental features like perspective. Binocular cues require both eyes to compare different viewpoints or track eye muscle movement.

How does convergence differ from accommodation?

Convergence is the inward turning of both eyes to aim at a near object, involving extraocular muscles. Accommodation is the change in the shape of a single eye's lens to focus light, involving the ciliary muscles.

When comparing relative size and linear perspective, which relies more on 'top-down' knowledge?

Relative size relies more on top-down knowledge because the brain must already know the typical size of an object to judge its distance. Linear perspective is more 'bottom-up' as it follows the geometric convergence of lines in the scene.

What is a common misconception about motion parallax regarding the number of eyes required?

Many people mistakenly believe motion parallax is a binocular cue because it involves complex movement. In reality, it is a monocular cue because the depth information comes from the change in a single eye's viewpoint over time.

Why is interposition considered a 'relative' rather than 'absolute' depth cue?

Interposition only tells you the order of objects (which is in front), but it provides no information about the actual distance between them. You know Object A is closer than Object B, but not by how many meters.

What error occurs if the brain fails to apply size constancy to a receding object?

If size constancy fails, the observer would perceive the object as physically shrinking in size as it moves away. This would lead to a distorted perception of reality where objects change their physical properties based on distance.

Define Retinal Disparity.

Retinal disparity is the slight difference between the right and left retinal images due to the horizontal separation of the eyes. The brain integrates these two images to create a single 3D perception with depth.

What is the 'Texture Gradient' cue?

Texture gradient is a monocular cue where a surface's pattern appears to become denser and less detailed as it recedes into the distance. This change in 'grain' provides a clear signal of increasing depth.

Define the concept of 'Relative Height' in depth perception.

Relative height is a pictorial cue where objects positioned higher in the visual field (closer to the horizon line) are perceived as being further away. This is most effective for objects located on the ground.

Why does retinal disparity become less effective as objects move further away?

As distance increases, the angle of light entering the eyes becomes nearly parallel, making the images in both eyes almost identical. Once the disparity becomes negligible, the brain can no longer use it to calculate depth.

Visual Cues & Constancies: Depth Cues | AQA GCSE Psychology

Visual Cues & Constancies: Depth Cues

Summary

Depth perception is the psychological process by which the brain transforms two-dimensional retinal images into a three-dimensional understanding of the world. This process relies on a combination of monocular cues (available to one eye), binocular cues (requiring both eyes), and oculomotor signals to calculate distance, volume, and spatial relationships.

1. Definition & Core Concepts

Depth Perception: This is the ability to perceive the world in three dimensions and accurately judge the distance of objects. It is a complex computational task because the retina only captures light on a flat, 2D surface, requiring the brain to 'infer' the third dimension.
Visual Cues: These are specific features in a visual scene or physiological signals from the eyes that provide information about depth. They are generally categorized based on whether they require one eye (monocular) or two eyes (binocular).
Perceptual Constancy: This is the tendency to perceive objects as unchanging (having consistent shape, size, and brightness) even as retinal images change. For example, size constancy allows us to understand that a car driving away is not actually shrinking, but simply moving further away.

2. Monocular (Pictorial) Cues

Linear Perspective: This cue occurs when parallel lines appear to converge at a single vanishing point in the distance. The greater the convergence of the lines, the further away the point is perceived to be by the observer.
Relative Size: If two objects are assumed to be of similar actual size, the one that casts a smaller retinal image is perceived as being further away. This relies on 'top-down' knowledge of what objects usually look like in the physical world.
Interposition (Overlap): When one object partially blocks the view of another, the blocking object is perceived as being closer. This is a powerful cue for determining the relative order of objects, though it does not provide absolute distance measurements.
Texture Gradient: Surfaces with a visible grain or pattern appear to have a finer, more densely packed texture as they recede into the distance. Closer areas show distinct details, while distant areas appear as a continuous, blurry mass.
Relative Height: Objects located higher in the visual field (closer to the horizon) are typically perceived as being further away than those lower in the field. This cue is particularly effective for objects resting on the ground plane.

Diagram showing linear perspective with a road converging at a vanishing point and two red squares illustrating relative size.

3. Binocular & Oculomotor Cues

4. Motion Cues

Motion Parallax: As an observer moves, objects at different distances appear to move at different speeds across the retina. Objects that are closer seem to zip by very quickly in the opposite direction of movement, while distant objects appear to move slowly or stay nearly stationary.
Deletion and Accretion: These occur when one object moves in front of another, causing parts of the farther object to be hidden (deletion) or revealed (accretion). This provides dynamic information about the relative depth and edges of objects in a scene.

5. Key Distinctions

6. Exam Strategy & Tips