Final answer:
The distraction hypothesis, which posits that cellphone usage diverts attention from driving, has the most supporting evidence regarding its negative impact on driving performance.
Step-by-step explanation:
The hypothesis that has received more supporting evidence regarding the negative effects of cellphone conversations on driving is the distraction hypothesis. This hypothesis suggests that the primary reason for decreased driving performance while using a cell phone is that the driver's attention is being diverted from the task of driving to the conversation at hand. Supporting evidence for the distraction hypothesis can be seen through research indicating that texting and holding cellphone conversations while driving can significantly impair response times, as drivers are less able to focus on the road and react to sudden changes, such as a leading car hitting the brakes.
Furthermore, psychologists have recognized the powerful influence of habitual behaviors, or event schemata, such as checking the phone, which can be hard to resist even while driving, thus causing distractions that can lead to accidents.