Perception and organisation

Perception is the process of giving meaning to the information our senses collect. It is not a simple copy of the world: we construct it, using what we know and expect. Draw the number 6 on the ground; a friend standing on the other side reads it as 9. The marks are the same; the meaning depends on the viewer.

Two ways of processing:

• Bottom-up: recognition starts from the parts and builds up to the whole. Looking at a stranger, you notice the uniform, the badge and the cap, and conclude: a security guard.
• Top-down: recognition starts from the whole and moves to the parts, guided by knowledge and expectations. You first see 'a person waving' from far away, then make out the face of your cousin.
• The two work together in everyday perception.

The perceiver matters. Several things inside us shape what we perceive:

• Motivation: our needs and wishes colour what we see. A student anxious to see results may read every notice on the board as the results list.
• Expectations (perceptual set): we perceive what we expect. If the doorbell rings at the time a parcel is due, you are sure it is the delivery.
• Cognitive styles: field-dependent people perceive the world in a global, whole way and find it hard to separate an object from its background; field-independent people break the scene into smaller parts and pick out details easily.
• Cultural background and experience: people raised in different settings learn to notice and interpret different things.

Gestalt psychologists argued that we perceive organised wholes, and that the whole is different from the sum of its parts. A text message 'gr8' is read as 'great'; a few dots in a circle look like a face.

Figure and ground. We see some part of a scene as the figure, standing out from the ground (background). The figure has a definite shape, looks closer and is better remembered; the ground is shapeless and seems to continue behind it. In some drawings the two can swap: the same black-and-white pattern is seen as one shape, then as another, but never both at the same moment.

Principles of perceptual organisation:

• Proximity: things close together in space or time are grouped (desks pushed together look like one group).
• Similarity: similar things are grouped (players in the same jersey are seen as one team).
• Continuity: we follow smooth, continuous lines rather than sudden changes in direction.
• Smallness: smaller areas tend to be seen as the figure, larger ones as the ground.
• Symmetry: symmetrical areas tend to be seen as figures.
• Surroundedness: an area enclosed by another is seen as the figure.
• Closure: we fill gaps and see incomplete shapes as complete (a circle drawn with a small break is still seen as a circle).