A researcher wishes to define the receptive field for a particular neuron in the visual cortex. To do this, the researcher will need to specify

an area within the visual field wherein the cell will fire if the target appears.

Explanation:

In order to accomplish this, the researcher will need to specify an area within the visual field wherein the cell will fire if the target appears. This is because there are about 100 billion neurons in the human brain and each of them fires at a speed of about 200 times per second, thus making it impossible to define the receptive field of a particular neuron without highlighting a specific area of that neuron and visualizing that specific neuron.