The answer is "the least amount of information that's necessary to understand a stimulus is actually present." The average amount of information that's necessary to understand a stimulus is actually present holds no relevance in psychological terms, while the amount of stimulus that's necessary to determine if a stimulus has been changed is called the difference threshold. The other answers hold no actual meaning in psychological terms, such as the max amount of stimulus, or the difference in stimulus to determine if the stimulus has been kept the same. 

Mania and anxiety are most closely associate with behavior and not sensory perception. The main difference between delusions and hallucinations are that delusions are false beliefs. Conversely, "hallucinations" are false perceptions from a stimulus that does not exists. These perceptions are generated by the mind and occur during consciousness. 

Absolute threshold is the lowest level of stimulation that an organism can detect. For example, the quietest sound that a human can hear is their absolute threshold for hearing.

Top-down processing involves the impact of prior knowledge on sensation and perception. Many optical illusions are successful by capitalizing on our prior knowledge to influence our perception of an image.

Selective attention allows one to focus on certain specific sensory information, while ignoring other sensory input. All of the given examples would require selective attention, and in fact, almost every situation you could imagine would require some level of selective attention. For example, when reading a book, even if you are in a quiet room, you require selective attention to focus on the pages and words while ignoring any sort of background noise or action in your periphery. 

The cocktail party effect explains one's ability to focus one's attention on one particular sound (an auditory stimulus) while simultaneously filtering out others. The name for this effect comes from the ability of a person at a party to focus his attention onto a particular conversation, while drowning out the other conversations happening at the party.

The cocktail party effect describes a person's ability to attend to just one voice among a group of voices--akin to a party guest's ability to listen to just one person's voice among the voices of many conversations. 

Jeff's knowledge that the amount of juice stayed constant is evidence that he understands conservation. According to Piaget, a child's understanding of the conservation concept is characteristic of the concrete operational stage, as this stage marks the start of logical and operational thinking. 

Top-down processing involves processing information by utilizing prior knowledge and conceptual knowledge of the whole. This allows the perception of how the smaller pieces make the whole. Timmy sees the whole, assembled structure of the engine in order to understand the workings of the spark plugs. Had he looked a spark plug, then attempted to figure out the workings of the engine, that would have been bottom-up processing.

Inattentional blindness describes the ability of the human mind to block out all but a single, deeply focused on piece of sensory input. The sudden sensory input of the dog in front of his car caused Sam's focus to narrow so significantly that he was inattentonally blind to the car next to him. The cocktail party effect, on the other hand, describes a person's ability to single out one voice among many in a room, and even to shift that focus, picking individual sounds on which to focus in a noisy room.