The concept of optimal arousal is visually represented by a line graph plotting 'performance quality' on the y-axis against 'arousal level' on the x-axis. The single curve is at its lowest point when both arousal and performance are low, indicating boredom or apathy. The curve peaks at an optimal level when both arousal and performance are medium. Finally, the curve drops to a low point when arousal is high and performance is low, indicating a state of high anxiety.