Explain what perception is and how it is guided by cognition (pp. Condillac (1715-1780) believes that if sensation doesn"t exist, there would no mental life. Sensation + perception = basics of cognition. Providing the brain an interpretation of the external world, as these stimuli are analyzed. Sensory input does not contain enough information to explain our perception (cube) Searching helps to del with the excess of input (painting, dog) Selective attention - choose part of sensory input for further processing in the expense of other aspects of that input. (painting, dog) Identify the structures of the visual system, including the dorsal and ventral pathways (pp. Visual scene forms an image on the retina, the layer of cells that respond to light, photoreceptors, and nerve cells at the back of the eye. Light is converted into electrochemical signals, transmitted to brain via optic nerves. Optic nerve = a bundle of the long axon fibers of the ganglion cells in retina.