A gradient of texture density: 
the projection of the people’s 
faces as they crowd the Coney 
Island beach is increasingly 
dense from the bottom to the 
top of the picture.

Gibson argued that perceptions 
such as those of planes in depth 
and constancy of size are based 
on more abstract features of the 
stimulus than earlier workers 
in the psychophysical tradition 
had considered. For example, it 
was maintained that the 
stimulus correlate of our 
perception that the plane of the 
ground recedes into depth is a 
gradient in the texture in that 
plane, not the appearance of 
separate objects located at 
different distances from one 
another on that plane. In the 
photograph to the left, the 
density of the faces of people 
standing on the beach 
increases from the bottom of 
the picture (representing the 
foreground) to the top 
(representing the more distant 
ground). This texture-density 
gradient is the stimulus for the 
plane of the ground, and the 
steepness of the gradient is the 
stimulus for its apparent slant.