During the night there may be many external stimuli bombarding the senses, but the brain often interprets the stimulus and makes it a part of a dream in order to ensure continued sleep. Dream incorporation is a phenomenon whereby an actual sensation, such as environmental sounds, are incorporated into dreams, such as hearing a phone ringing in a dream while it is ringing in reality or dreaming of urination while wetting the bed. The mind can, however, awaken an individual if they are in danger or if trained to respond to certain sounds, such as a baby crying. Except in the case of lucid dreaming, people dream without being aware that they are doing so. Some philosophers have concluded that what we think of as the "real world" could be or is an illusion (an idea known as theskeptical hypothesis about ontology). There is a famous painting by Salvador Dalí that depicts this concept, titled "Dream Caused by the Flight of a Bee around a Pomegranate a Second Before Awakening" (1944). The first recorded mention of the idea was by Zhuangzi, and is also discussed in Hinduism makes extensive use of the argument in its writings. It was formally introduced to Western philosophy by Descartes in the 17th century in his Meditations on First Philosophy. Stimulus, usually an auditory one, becomes a part of a dream, eventually then awakening the dreamer. The term "dream incorporation" is also used in research examining the degree to which preceding daytime events become elements of dreams. Recent studies suggest that events in the day immediately preceding, and those about a week before, have the most influence.