Central and Peripheral Vision The receptive field of a neuron in the visual system is the part of the visual field that an individ ua l neuron "sees “that is, the place in which a visual stimulus must be located to produce a response in that neuron. The location of the receptive field of a particular neuron Depends on The location of the photoreceptors that provide it with visual information. If a neuron receive information from photoreceptors located in the fovea, its receptive field will be at the fixation point-the point at which the eye is looking. If the neuron receives information from photoreceptors located in the periphery of the retina, its receptive field will be located off to one side. Fovea and Periphery At the periphery of the retina Many individual receptors converge on a single ganglion cell→, bringing information from a relatively large area of the retina- and hence→ a relatively large area of the visual field. However, the fovea contain approximately equal numbers of ganglion cells and cones. These receptor-to-axon relationships explain the fact that Our FOVEAL (CENTRAL) VISION is very ACUTE But PERIPHERAL VISION is much LESS PRECISE. (See Figure 6.8.) Types of eye movements To keep stimuli from the environment projecting to the retina, particularly the fovea, the eyes make three types of movements: Vergence movements, saccadic movements, and pursuit movements. Vergence movements are cooperative movements that keep both eyes fixed on the same target-or, more precisely, that keep the image of the target object on corresponding parts of the two retinas If you hold up a finger in front of your face, look at it, and then bring your finger closer to your· face, your eyes will make vergence movements toward your nose. If you then look at an object on the other side of the room, your eyes will rotate outward, and you will see two separate blurry images of your finger. When you scan the scene in front of you, your gaze does not roam slowly and steadily across it feature, Instead, your eyes make jerky saccadic movements. You shift your gaze abruptly from one point to another. When you read a line in this book, your eyes stop several times, moving very quickly between each stop. You cannot consciously control the speed of movement between stops; during each saccade the eyes move as fast as they can. Only by performing a pursuit movement—say, by looking at your finger while you move it around—can you make your eyes move more slowly. (In Chapter 9), you’ll read about rapid eye movements that occur during REM sleep. These movements are saccades that occur during dreaming and correspond with self-reports of visual imagery in the dreams of awakened sleepers .Other researchers have suggested that the saccades in REM sleep may trigger dream images.
