Figure 1.

Tuning properties of single neurons and definitions of invariance. (A) The tuning of one simulated neuron for retinal stimulus position (horizontal and vertical dimension in the colour matrices) as assessed with two shapes and two different sizes. The position and size sensitivity of this simulated neuron is representative for empirically measured tuning properties in monkey inferior temporal cortex. (B) The ‘relative invariance’ of tuning for multiple dimensions can be assessed by ranking stimuli that vary on one dimension based on the response strength at one value of a second dimension, and then verifying whether this stimulus preference is the same at another value of this second dimension. Here this phenomenon is illustrated with shape (left panel) or size (right panel) as the first dimension of which the values are being ranked, and retinal position as the second dimension. (C) The ‘independence’ of tuning for multiple dimensions can be assessed by comparing the joint 2-D tuning with the marginal tuning in which the tuning for one dimension is plotted averaged across all values of the other dimension. The left panel illustrated independence of tuning, the right panel a high degree of dependence.