Final answer:
Reaction times for the left hand are shorter when stimuli are presented on the left because of brain lateralization, where the right hemisphere processes sensory information and controls the motor functions for the left side of the body, resulting in faster response times. Additionally, handedness may play a role as the dominant hand usually has more refined motor skills.
Step-by-step explanation:
The shortened reaction times for the left hand, when the target stimulus is presented in left space compared to right space, can be attributed to the brain lateralization and the specific connections between the brain's hemispheres and the contralateral sides of the body. The left hemisphere of the brain, which is dominant for language functions in 95% of the population, controls the motor functions of the right side of the body and processes sensory information from the right side. Similarly, the right hemisphere controls the left side. Because of this arrangement, motor commands and sensory inputs are more directly connected for the dominant side of the brain with its respective contralateral side, leading to a faster response time. Therefore, a left-handed stimulus would be processed quickly by the right hemisphere, which controls the left hand.
In contrast, the cognitive development of handedness indicates a preferred use of one hand over the other, potentially affecting reaction times. Individuals' dominant hands are generally faster and more accurate due to more frequent use and fine-tuning of motor skills.