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Human brain receives a variety of raw data through sense organs, and process them to generate meaningful information like an image or an alarm etc. These environmental information is passed to and integrated in cerebral cortex, where it is evaluated with respect to knowledge acquired from previous experiences. Finally, if the situation warrants an effort for a reward or survival, a strong signal is generated. This signal activates primary motor cortex for movement and control of limbs, thus playing a vital role in subsequent action. We call this Perception, mechanism to be Aware. A bottom-up processing of the raw sensor modalities to form an abstraction of the environment, combined with a top-down processing of the memory and knowledge acquired through previous experiences, are involved in the complex process of Perception. The time lag between external stimuli and corresponding action is reaction or reflex delay, consisting of occurrence of external stimuli to its perception (Tper) and perception to action (Tact). We are interested to measure Tper, the perception delay. When a strongly desired or acutely dangerous event, which occurs with low probability, a large number of neurons in the parietal lobe exhibit synchronized activity, producing a signal strong enough to detect outside the skull using electroencephalography (EEG). We define the onset time of perception signal, and measure Tper for different subjects. We also indicate how our method of analysis of EEG signal could usher efficient Brain Computer Interface (BCI) applications.