The Singapore Theory
It's important to approach research from as many view points as possible, and to be open minded when it comes to embracing a variety of research methods and theories.
The Singapore Theory (also referred to as the Theory of Familiarization or simply Paranormal Stimuli) is, in essence, really basic.
The method involves trying to recreate the environment, or a part of the environment, of a particuliar era during an investigation in an attempt to stimulate paranormal activity. The theory is based on familiarisation and the belief that if spirits occupying a location, or in attachment to an object, recognize the environment or something within it, they will become active and possibly show themselves in some form. In the case of residual energy/hauntings, it may be that relevant external factors created by the living could potentially trigger the 'recording' or imprint to play.
Playing period music, wearing period outfits, burning oils, incense or using a fragrance familiar to a time period (coal for example or to an individual person (tobacco etc) and the use of trigger objects can all be considered implementation of The Singapore Theory. More complex implementation may involve the total recreation of a site, using furnishings and anything else possible. In some cases a complete re-enactment/reconstruction of the traumatic event that is believed to have caused the haunting, such as a murder, has been undertaken.
Many investigators believe that the type of activity that is stirred up by Singapore Theory is of a residual nature, rather than an "intelligent haunt". In order for a residual haunting to manifest, conditions must be just right, and this will of course vary. By recreating an environment that mimics that which was present when the "haunting" originated could well be enough to set those conditions in motion and make it ideal for a manifestation. This also runs parallel to some degree with The Stone Tape Theory.
The degree to which you attempt the Singapore theory yourself will obviously depend on resources, but even identifying small clues to the life and times of a potential spirit can assist you in making a connection. Be imaginative, and who knows what may happen!