1. Figure and ground
Psychologists use the terms figure and ground to label an object and its background respectively.
The classification of an item as a figure or as part of the background depends on the behaviour of the observer, it is not an intrinsic property of the item.
In the image on the slide the figure and ground can be reversed. You can see either two faces against a white background or a goblet against a dark background.

2. Form perception and boundaries
One of the most important aspects of form perception is the existence of a boundary. If the visual field contains a sharp and distinct change in brightness, colour or texture, we perceive an edge. If this edge forms a continuous boundary, we will probably perceive the space enclosed by the boundary to be a figure.

3. The principles of Gestalt
Grouping - We tend to perceive a group of smaller elements as a larger figure.
Illusory contours. Even when boundaries are not present, we can be fooled into seeing them.
Proximity. Different spacing of the dots produces five vertical lines or five horizontal lines.
Similarity. Similar elements are perceived as belonging to the same form.
Good continuation. It is easier to perceive a smooth continuation than an abrupt shift.
Closure. We tend to supply missing information to close a figure and separate it from its background.

4. A letter search task
Perception involves analysis of distinctive features.
This slide shows an example of a letter search task used by Neisser (1964); it shows two columns of letters. Participants are required to search through the columns until they find the letter Z which occurs once in each column.
It is easier to find the Z in the left column (which is comprised of letters sharing few features in common with the target letter) than it is to find the Z in the right column (which is comprised of letters sharing many features in common with the target letter).
Source: Adapted from Neisser, J., Scientific American, 1964, 210,

5. Geons for perception
Biederman (1990) suggests a model of pattern recognition that combines aspects of prototypes and distinctive features. He suggests that the shape of objects that we encounter can be constructed from a set of 36 shapes that he calls geons.
This slide shows five geons (a) and some objects that can be constructed from them (b).
Source: Adapted from Biederman, I., Higher-level vision. In An Invitation to Cognitive Science. Vol. 2: Visual Cognition and Action, edited by D.N. Osherson, S.M. Kosslyn and J. Hollerbach. Cambridge, MA: MIT Press, 1990.

6. Distinctiveness and attractiveness
This slide shows faces similar to those used by Perrett et al (1994).
The photographs in the experiment were constructed by averaging across a selection of photographs that had themselves been rated as attractive. The final averaged photograph was then enhanced to provide a ‘highly attractive’ composite.
The faces on the slide are ‘morphed’ from averagely attractive (starting at the left) to very attractive (on the right).

7. The principal monocular and binocular depth cues
We perceive the distance of objects from us and from each other by using monocular and binocular cues.
Binocular cues arise from the fact that the visual fields of both eyes overlap; only animals with eyes on the front of the head can use these.
Animals with eyes on the side of the head can only use monocular cues.
Pictorial cues – can be represented in a drawing or photograph.
Motion parallax – changes in the relative locations of objects give cues about their distance.
Convergence – when the eyes converge on a near object, the angle between them is greater than when they converge on a distant object.
Retinal disparity – the amount of disparity produced by the images of an object on the two retinas gives a clue about its distance.
Examples of pictorial cues:
Interposition – an object placed between us and another object, that partially obscures our view of the other object, must be closer to us.
Size – knowing the size of objects enables us to judge their distance.
Linear perspective – parallel lines that recede from us appear to converge at a single point.
Texture – coarser textures look closer, fine textures look distant.
Haze – distant landscapes become less distinct because of haze.
Shading – the top of a convex object will be light, the bottom will be in shadow.
Elevation – we perceive objects near the horizon as being distant from us and those above or below it as being nearer to us.
Source: Adapted from Matlin, M.W. and Foley, H.J., Sensation and Perception (3rd edition). Boston: Allyn & Bacon, 1992.

8. Some pictorial cues to depth 1
Perspective - this gives the appearance of distance and makes the two columns look similar in size.
(b) Haze - variation in detail, owing to haze, produces an appearance of distance.
Source: (b) Powerstock, reprinted by permission.

9. Some pictorial cues to depth 2
(c) Shading - if the tops of the circles are dark, they look like depressions. If the bottoms are dark, they appear as bumps.
(d) Elevation - The objects nearest the horizontal line appear furthest away from us.
Source: (d) Adapted from Martin, M.W. and Foley, H.J., Sensation and Perception (3rd edition). Boston: Allyn & Bacon, 1992.