Final answer:
To perceive a difference between two stimuli, a change must exceed the just noticeable difference (jnd) or difference threshold, as described by Weber's law. Factors such as attention, motivation, and signal detection theory significantly influence our ability to detect and perceive stimuli.
Step-by-step explanation:
To perceive a difference between two stimuli, we rely on the concept of the just noticeable difference (jnd) or difference threshold. This is the minimum amount of change in a stimulus that must occur for our sensory receptors to detect a difference. Ernst Weber formulated Weber's law in the 1830s which states that the jnd is a constant fraction of the original stimulus. Therefore, for a person to notice a difference between two stimuli, the change must be proportionally significant compared to the initial intensity of the stimulus.
Our perceptions are not only influenced by these thresholds but also by factors such as attention, motivation, sensory adaptation, cultural context, and prior experiences. For instance, if someone is motivated to detect a particular stimulus, like a mother listening for her baby, they are more likely to perceive it, even if it is relatively quiet compared to other noises. This is partly explained by signal detection theory, highlighting how our perception can shift based on these psychological factors.
Attention plays a crucial role as well; when we focus our attention on certain stimuli while ignoring others, this selective attention process determines what we perceive. For instance, at a party, you may engage in a conversation and tune out background noise, demonstrating how your focused attention influences your sensory perceptions.