Phenomena Relating to Danger, Death, Bereavement

In recent years, a variety of anomalous perceptual phenomena have been noted that appear to be triggered by crises relating to danger, death and bereavement. Research into these phenomena has gathered momentum in the last decade, as it becomes clear that the prevalence rate of reported experience is substantial.

Crisis Impressions

Crisis impressions are marked by the abrupt awareness that another person is in urgent danger or has died. These are also referred to as ‘crisis apparitions,’ a term used by late nineteenth century psychical researchers, although visual manifestation is not necessarily a defining characteristic. Studies by Gurney et al1, Green,2 Stevenson,3 Fenwick4 and Haraldsson5 have highlighted cases where action was taken as a result of the impression, but before conventional news of death or danger had been delivered to the percipient. Stevenson, most recently, studied only those cases that could be corroborated by witnesses. (The percipient demonstrably reacted to the impression – by putting through an urgent phone call, for example, or rushing home.

Crisis Impressions take a number of forms:

Visual perceptions 

Percipients report the sudden manifestation of a person at or near the time of that person’s death. These occur in waking states, irrespective of lighting conditions.6 Examples: A woman working out at the gym suddenly perceives her partner standing before her in what appears to be full, three-dimensional solidity. Yet the perception occurs at the time that her partner is actually being crushed by rock fall on a glacier whilst mountain climbing.7 A man reports seeing his father seated at the breakfast table in the family kitchen, even as news is delivered to him that his father has just died.8

Impressions can take symbolic rather than literal form. Chaz Ebert, wife of film critic Roger Ebert, told of awaking to find the figure of death at her bedroom door: the figure pointed to a coffin that was lying on her bed and contained her ex-father-in-law, who was not yet known to have died that night.9

Another example of a symbolic image pertains to a British navy sailor at sea, who was lying on his bed when he suddenly hallucinated teletype text that announced the death of his grandfather in England.10 

In 1942, researcher GNM Tyrell identified 130 cases of collective visual perception, where more than one person saw the same impression at the same time.11 Tyrell analyzed the cases researched and presented in the 1886 two-volume set, Phantasms of the Living.12

Intuitive Gleanings  

In this type of impression, a sudden and specific conviction that someone is in danger prompts the percipient to take action. An early example was reported by Hans Berger, inventor of the EEG. At a moment when he was nearly run over by a horse-drawn cannon his sister felt such overwhelming anxiety concerning his safety that she urgently arranged for a telegram to be sent to him enquiring after his wellbeing. Struck by her insistent concern, Berger subsequently devoted his time to inventing a machine that would measure electrical activity in the brain, believing that this might reveal a means of human-to-human connection.13

A series of 35 cases investigated by psychiatrist Ian Stevenson in the 1960s included that of an American woman who was abruptly beset by the conviction that her daughter had been hit by a car. She immediately telephoned the destination where her child had been heading, and learned that a (non-fatal) collision had occurred during the journey.14

Somatic impressions  

Cases have been collected of what appear to be shared illness and dying symptoms at the onset of the crisis. One example, reported to neuropsychiatrist Peter Fenwick, involves a man who, at the time that his dying father was drawing his last breaths, was roused from sleep by intense feelings of suffocation.  'I remember grabbing my mouth, forcing it open to help me breathe. I was fighting for all I was worth, but the pains were now unbearable.' 15 Similar cases have been reported in relation to symptoms of fatal heart attack, and accidental injury.16

Emotional impressions

Reports exist of an inexplicable shift in mood at the instant of a distant death, such as being overcome by sobbing, or conversely, experiencing elation and almost transcendental feelings of peace. Key features are the abrupt onset of the mood, lacking any apparent trigger, and its coinciding with the as-yet unreported death. Researchers have attempted to preclude cases where chronic mood instability happens to coincide with a crisis, or where ‘repeated, gloomy forebodings in one instance turn out to be true.’17 

Dream Impressions  

Individuals have a vivid and distinct dream that alerts them to the death of someone close to them. The dream can feature details of the death or a visit from the deceased, bidding goodbye or offering reassurance. Fenwick reports the case of a woman who had a dream encounter with her ex-husband on the night of his suicide. It was sufficiently clear that she cancelled her morning work appointments, explaining that a death had occurred; then she went to his house, where she found his lifeless body and telephoned the police. 

Prevalence Data

 A sizeable body of cross-cultural research establishes the prevalence of perceived encounters with the deceased among the bereaved at between 43% and 55%.18 It is less clear how many of these encounters constitute crisis impressions. An Icelandic study determined that 86% of encounters constituted the first intimation that a death had occurred.19 In Germany, 'Crisis ESP' was found to be among the most commonly reported types of spontaneous psi perception. In the UK, a 2010 survey of hospice staff reported that half of respondents were aware of ‘coincidences usually reported by friends or family ... who say the dying person has visited them at the time of death.’20 A disproportionate number of crisis impressions occur in connection with violent or sudden deaths, according to two studies.21 There is a clear need for further research in this area in order to evaluate the data.

Alternative theories 

There is no psychological theory for crisis impressions, as such, but it would certainly be argued that they are wishful reconstructions of subjective experience after a death or danger has come to light. An example would be the mental process of ‘convergence during recall’, where ill-fitting details fall away as a dream or waking experience aligns with new information. No study has been done to determine the precise nature of this act of reconstruction specifically in relation to crisis impressions. Research has tended to focus on the broader concept of ‘psychology of belief’ without specifically addressing time-of-death perceptions.22

Deathbed Visions

A growing body of research explores a distinct category of both visual and auditory phenomena perceived by dying patients in the last days of their life. This research has garnered attention as Westerners move in ever greater numbers into hospice care, an environment in which they are often observed by family and caregivers when their pain is well-managed and their consciousness is clear. A 2013 American study reported that hospice nurses witness, on average, five patients experiencing ‘deathbed communication’ with one or more unseen figures each month.23 Penny Sartori, a British researcher and former critical care nurse, has said that nurses sometimes informally regard such incidents as an indication of the patient’s imminent death.24 In 2014, the American Journal of Hospice and Palliative Care reported a study in which more than 80 percent of dying patients experienced visions and dreams over an eighteen month period.

While deathbed visions have been noted throughout history, a first wave of interest in them by secular scholars took place in the early twentieth century, with publications such as Ernesto Bozzano’s Apparitions of Deceased Persons at Deathbeds (1906), James Hyslop’s Visions of the Dying (1907), andWilliam Barrett William Barrett’s Deathbed Visions (1924).25 These visions differ from biologically-mediated hallucinations in relation to their timing, their non-random specificity, their occurrence in states of clear consciousness, and their observed psychological impact on the dying.26

Take-away Companions

A significant feature of the deathbed vision is the perception of figures – typically deceased relatives or totemic religious figures – who seem to cause the dying person to light up, to reach forward and/or to communicate with a presence undetected by others in the room. On the other hand, some cases have been reported where the dying person was unaware that the person they were seeing was no longer alive. In  an early case of this type reported by Barrett, his obstetrician wife was attending the bedside of a woman who was dying following childbirth. She and three others saw the woman express delight at suddenly seeing her deceased father, but also puzzlement at seeing her sister Vida, whose death three weeks earlier had been kept from her for fear of damaging her health. 27 These are known as Peak in Darien experiences,28 referencing the astonishment that Spanish explorers felt when they climbed a mountain in Panama expecting to discover the continent of India, and instead beheld the Pacific ocean.

In the largest cross-national study of deathbed visions, cases were found in which the percipient did not expect to be dying, as they had no terminal prognosis, and yet they did die shortly after having the vision. This study29 found no correlation with levels of drug sedation or psychological expectation.

Another feature of deathbed visions reported by patients to hospice staff and family members is a perception of light or beauty, described in such terms as, ‘if you could only see what I see’, and ‘I am melting into all this beauty’. This aspect is largely anecdotal, and remains to be researched.30

Compared to Medically-mediated Hallucinations.

The ingestion of morphine, or other pain-management medications known to have consciousness-altering properties, is widely supposed to play a role in death-bed visions. However, this correlation is not supported by research. The single significant cross-national study to examine causative variables found that just twenty per cent of patients who saw deceased loved ones or totemic figures at the end of their lives were under strong levels of sedation. Pharmaceutical sedation was found generally to create the opposite effect, making such visions less likely to occur.31

In two recent British studies and a Canadian study, hospice staff drew a distinction between the hallucinations induced by medication, which tended to be unsettling and idiosyncratic, and those involving take-away companions, which appeared to bring calm and reassurance to dying patients, as they ‘learned who they were to go with’.32

Sensed Presence Phenomena

The presence that is visualized, sensed or heard in both crisis impressions and deathbed visions has been reported in other environments also: where percipients are themselves in danger or psychological distress, or where they have been bereaved.  The categories can overlap, as in the case of World War I soldier William Bird, who was awoken in the trenches by his deceased brother, who insisted that he rise, escorted him out of his tent and well away from it, and disappeared; the tent was then obliterated by a shell.33

‘Third Man’ 

The phenomenon of sensing an invisible, yet accompanying, presence while traversing physically challenging landscapes is well established in mountaineering literature. This presence has been dubbed ‘the Third Man’, in reference to a poem by TS Eliot that mentions a presence sensed during the 1916 Antarctica expedition led by Ernest Shackleton, and has been frequently reported by mountain climbers, polar explorers, sea voyagers, cave explorers and deep-sea divers. There are also multiple reports in theatres of war. A typical example is described by John Geiger, head of the Canadian Geographic Society, in his book The Third Man Factor (2008).

Amerian climber James Savigny was severely injured by an avalanche in British Columbia in 1983. His back, arms and ribs were broken and he was bleeding internally. He could not stand, and began succumbing to shock and hypothermia. At this point, he sensed a presence. It directed and prodded him over ice-ridden terrain back to his camp. 'All decisions made were made by the presence, I was merely taking instructions.' When he reached his tent, the presence vanished. He was later found and rescued by cross-country skiers.34

Sensed Presence During Danger in Non-extreme Environments.

This experience is similar to the Third Man, occuring in moments of danger but where the percipient’s body is under no biological or functional duress. In other words, it cannot be explained in terms of sensory deprivation, high altitude, or neurological factors, such as the well-established syndrome of physical disruption to the Tempero-Parietal Junction that leads to a confused sense of self versus Other.35 Cases are found in testimonies of rape victims and people who are caught in (but unharmed by) house fires, also during critical moments of decision-making that enable the avoidance of danger. Thus far, numerous testimonies exist in the context of book-length research, but no formal academic study has been done.36

Post-mortem presences

There is now an extensive body of research, particularly within grief literature, on the prevalence of sensed presence encounters within the bereaved population. Estimates range from 43% to 55%, with some countries reporting even higher rates.37 The research shows no consistent correlation to social isolation, mental health, depth of attachment or length of grieving period, all of which have been proposed as psychological variables that could account for ‘grief hallucinations’.

In a typical case collected by journalist Patricia Pearson, a widow in New Mexico reported feeling the presence of her partner in their bed on two separate occasions, at five months and four years, after his death in 2002, saying 'I feel pressure on the mattress, so strong that I roll over to see who is there.'

In another case reported to Pearson, a Toronto advertising executive describes the specific and vivid entrance of her deceased father’s presence into the car she is driving. She feels the weight in the car being redistributed as he settles into the passenger seat in his characteristic manner, leaning in a particular way to avoid getting back pain. He remains for twenty minutes, during an hour-long commute from work to home. It is six weeks after his death.38

Nearing-Death Awareness

In 1993, hospice nurses Maggie Callanan and Patricia Kelly coined the phrase ‘nearing-death awareness’ to describe anomalous characteristics that palliative care staff sometimes observe in their patients in the days preceding death.39 One such is the ‘deathbed vision' cited above, in which the patient communicates with deceased figures in the room, or describes their presence. There are two other  characteristics of note:

‘Journey’ References

As has been reported in several American and British studies, palliative and hospice staff often observe a preoccupation with travel and movement in the dying.40  This takes the form of pragmatic requests: for help to put their shoes on, to find their train ticket, to board the boat, bring the car around, go for a walk or simply to go home. These occur at a stage when their use of language in general has become limited and stark, and are therefore quite distinct from febrile mutterings. A near-comatose patient may unexpectedly utter a brief phrase about the trip they’re about to embark upon. Or they may ask, 'When am I going?' Studies show that the answer is invariably within two or three days, irrespective of medical prognosis. Paramedics and physicians have reported surprise at being told by patients that they ‘are leaving’ at a time when symptoms don’t appear to be terminal. In one study, carried out in a palliative care residence in Quebec, preoccupation with travel was found to feature in patients’ end-of-life dreams.41

Terminal Lucidity

In this phenomenon a person’s clouded consciousness briefly clears at the end of life, enabling patients who have been too neurologically, psychologically or cognitively disabled to suddenly communicate lucidly. For reasons that are not understood, such people suddenly regain mental clarity, to the extent of being able to have final conversations with family members or healthcare staff.42

Case reports of terminal lucidity date back to the nineteenth century and feature patients who are suffering, variously, from severe dementia, stroke, brain tumour, brain abscess, meningitis, psychosis, schizophrenia and mental disability. In a case reported by American oncologist Scott Haig in 2007, a patient with lung cancer had such profound metastasis to the brain that cerebral tissue was almost completely overtaken by cancer cells. He had become vegetative, with ‘no expression, no response to anything we did to him’. An hour before his death, he awoke, and spoke calmly and clearly to his wife and three children. 'It wasn’t David’s brain that woke him up to say goodbye that Friday,' Haig later wrote. 'His brain had already been destroyed.'43  In another case, reported in Germany in the 1930s, a severely mentally disabled woman named Anna Katharina Ehmer, institutionalized since infancy with no capacity to walk, speak or engage in rudimentary self-care, was observed singing a hymn about the transit of the soul, over and over to herself, in the hours before she died of tuberculosis. The nurses, her physician, and the director of the institution all witnessed this remarkable instance.

Numinous Experiences in Crisis and Near Death

Certain conditions appear to give rise to a state of consciousness that might be characterized as numinous. In this state, percipients feel themselves to be immersed in extremely brilliant light that they experience as loving, and possessed of a sentient quality, indicating that it is no merely visual perception. Feelings of profound peacefulness or joy generally accompany the perception.

During the Near Death Experience

The phrase ‘going into the light’ is most commonly associated with the Near-Death Experience (NDE). The experience it describes is one of the characteristics listed on the Greyson NDE Scale, which aims to ascertain if a clinically-defined (if poorly understood) subjective experience has taken place.44  Bruce Greyson, a Professor of Psychology at the University of Virginia until 2014, defines NDEs as ‘a profound psychological event including transcendental and mystical elements, typically occurring to individuals close to death or in situations of intense physical or emotional danger’. 

American naval engineer David Bennett described his encounter with this light while submerged in the Pacific Ocean: 'As I got closer (to it) I started feeling the light … I felt love, joy, passion and excitement ... As a chief engineer on a ship, I had many occasions to use an arc welder. The light emitted from the arc is so bright you have to wear protective eye gear to look at it without burning your eyes. This light was brighter than that, yet I could still view it comfortably.' Bennett adds, echoing a common element of the experience: 'Separating from the light and rejoining my body was the hardest thing I had ever been asked to do. It was more painful than drowning.'45

In the Absence of ‘Dying Brain’ Physiology

Although descriptions of transcendental light have long been associated with the NDE, they also appear in circumstances in which the percipient is not physically close to death. Research published in 2014 compared coma patients who reported having had an NDE with people who reported having an NDE-type experience during meditation, while fainting, after drug or alcohol consumption or in the midst of other non-life threatening situations. More than 75 per cent of the latter group reported NDE features, including an encounter with ‘a brilliant light’.46  Similar experiences have been reported by people who considered themselves to be in life-threatening danger which they ultimately avoided. Here, for example, is a description by Canadian physician Yvonne Kason, who survived, without serious injury, a plane’s crash landing on ice:  'I was like a drop of water which had now merged into the sea of light. I still existed, it was still me, but I was in this incredible ocean of light and love. The strongest aspect for me was the love. Perfect love. It’s impossible to describe.'47  The quality of ineffability – being unable to adequately describe the light – is common to all reports. This corresponds philosophically to what has been called the quandary of the Unsayable.48

Compared With Mystical States

German theologian Rudolf Otto characterized the experiences described by religious mystics as ‘numinous’.  By this, he meant an encounter with ‘divine power’ or ‘God’s majesty’, referencing the Latin word numen. It is an encounter, he wrote, that is ‘wholly other’, in that it features ‘strange ravishment … vitality, passion, emotional temper, will, force, movement’.49  A core element of this experience is sentient light, as described by sixteenth-century Spanish mystic Teresa of Avila: 'The splendor is not one that dazzles; it has a soft whiteness, is infused, gives the most intense delight to the sight, and doesn’t tire it; neither does the brilliance. It is a light so different from earthly light that the sun’s brightness that we see appears very tarnished in comparison with that brightness.'50 In her study of medieval NDE narratives religious studies scholar Carol Zaleski has found in accounts of the light a striking resemblance to contemporary testimony.51

Alternative Theories

Brain-based theories about subjective perception pertaining to this light, and the associated peacefulness, have focused on anoxic brain damage,52 sleep abnormalities related to REM intrusion,53 and the impact of sedative medication.54  Because some of these theories presuppose a physiology of brain trauma, they are difficult to reconcile with more recent research on the broader range of physically unimpeded percipients.

Patricia Pearson


Alvarado, C. (2014). An introduction to “Visions of the Dying” by James Hyslop. History of Psychiatry 25, 237.

Barbato, M. (1999). Parapsychological phenomena at the time of the death. Journal of Palliative Care 15.

Barrett, Sir W. (19262012). Deathbed Visions: How the Dead Talk to the Dying. Hove, UK: White Crow Books.

Bell, V. (2008). Ghost Stories: Visits from the DeceasedScientific American,  2 December. 

Blackmore, S. (1993). Dying to Live: Science and the Near-Death Experience. London: Grafton.

Brayne, S., Lovelace, H., Fenwick, P. (2008). End of life experiences and the dying process in a Gloucestershire nursing home as reported by nurses and care assistants. American Journal of Hospice and Palliative Medicine 25/3,195-206.

Callanan, M. and Kelly, P. (1992). Final Gifts: Understanding the Special Awareness and Communication Needs of the Dying. New York: Simon and Schuster.

Charland-Verville, V., Jourdain, J-P., Thonnard, M., Ledoux, D., Donneau, A-F., Quertemont, E., & Laureys, S. (2014). Near-death experiences in non-life threatening events and coma of different etiologies. Frontiers of Human Neuroscience, 27 May.

Coffey, M. (2008). Explorers of the Infinite: The Secret Spiritual Lives of Extreme Athletes. New York: Tarcher.

Cook, T. (2013) Grave beliefs: Stories of the supernatural and the uncanny among Canada’s Great War trench soldiers. Journal of Military History 77 (April).

Fenwick, P. & Fenwick, E. (2008). The Art of Dying. London: Continuum Books.

Fenwick, P., Lovelace, H., Brayne, S. (2009). Comfort for the dying: five year retrospective and one year prospective study of end of life experiences.  Archive of Gerontology and Geriatrics

Franke, W. (2014). A Philosophy of the Unsayable. South Bend, Indiana: University of Notre Dame.

Geiger, J. (2008). The Third Man Factor. Toronto: Penguin.

Greyson, B. (2010). Peak in Darien Experiences. Anthropology and Humanism 35/2, 159-71.

Gurney, E., Myers, F.W.H., Podmore, F. (1886). Phantasms of the Living. London: Truber.

Haig, S. (2007). The brain: The power of hope.  Time, January 29. 

Haraldsson, E. (2012). The Departed Among the Living: An Investigative Study of Afterlife Encounters. Hove, UK: White Crow Books.

Hawker, P. (2000). Secret Affairs of the Soul: Ordinary People’s Extraordinary Experiences of the Sacred. Northstone Publishing.

Lawrence, M. (2013). The incidence of deathbed communications and their impact on the dying process. American Journal of Hospice and Palliative Care. November, 30/7, 632-9.

Lopez, U. et al (2006). Near-Death Experience in a boy undergoing uneventful elective surgery under general anesthesiaPediatric Anesthesia 16/1, 85-8.

MacConville, U. (2012). Capturing the invisible: Exploring deathbed experiences in Irish palliative care presented at Afterlife Awareness Conference, Virginia Beach, Virginia.

Millett, D. (2001). Hans Berger: From psychic energy to the EEG. Perspectives in Biology and Medicine 44/4.

Nahm, M., Greyson, B., Kelly E.W, Haraldsson E. (2012). Terminal lucidity: A review and a case collection. Archives of Gereontology and Geriatrics, July-August 55/1.

Nahm, M, & Greyson, B. (2013-2014). The death of Anna Katharina Ehmer: A case study in terminal lucidityOmega 68/1, 77-87.

Nelson, K.R. et al (2006). Does the arousal system contribute to near-death experience? Neurology 66/7, Apr 11, 1003-9.

Nosek, C. (2015). End-of-Life Dreams and Visions. American Journal of Hospice and Palliative Medicine 32/3.

Osis, K. and Haraldsson, E. (1971/2012). At The Hour of Death: A New Look at Evidence for Life after Death. Hove, UK: White Crow Books.

Otto, R. (1917/2012). The Idea of the Holy. Forgotten Books.

Pearson, P. (2014). Opening Heaven’s Door: What the Dying May Be Telling Us About Where They’re Going. New York: Atria.

Seguin, M. (2009). Les Reves en Fin de Vie: 100 Recits de Reves pour Faciliter la Grande Traversee. Quebec: Flamarion.

Singh, Dowling, K. (2000). The Grace in Dying: A Message of Hope, Comfort and Spiritual Transformation. San Francisco: Harper.

Steffen, E. and Coyle, A. (2012). Sense of presence experiences in bereavement and their relationship to mental health: A critical examination of a continuing controversy. In Mental Health and Anomalous Experience, ed. by C. Murray, 33-56. Hauppauge, NY: Nova Science Publishers.

Stevenson, I. (1973). Telepathic Impressions: A Review and Report of 35 New Cases. Charlottesville: University of Virginia Press.

Terkel, S. (2001). Will the Circle be Unbroken?: Reflections on Death, Rebirth and Hunger for a Faith. New York: Ballantine.

Tyrell, G.N.M. (1943/1973). Apparitions. London: Society for Psychical Research.

Underhill, E. (1919/1999). Mysticism: The Preeminent Study in the Nature and Development of Spiritual Consciousness. London: Oneworld Publications.

Zaleski, C. (1987). Otherworld Journeys: Accounts of Near-Death Experiences in Medieval and Modern Times. Oxford University Press.


  • 1. Gurney et al (1886)
  • 2. Green (1960), Rhine,Rhine 1981.
  • 3. Stevenson (1973).
  • 4. Fenwick & Fenwick (2008).
  • 5. Haraldsson (2012).
  • 6. Haraldsson (2012).
  • 7. Coffey (2008).
  • 8. Pearson (2014).
  • 9. Terkel (2001)
  • 10. Fenwick (2008).
  • 11. Tyrell (1943/1973).
  • 12. Gurney et al (1886).
  • 13. Millett (2001).
  • 14. Stevenson (1973).
  • 15. Fenwick (2008).
  • 16. Hawker (2000).
  • 17. Stevenson (1973).
  • 18. Steffen and Coyle (2012); Barbato (1999).
  • 19. Haraldsson (2012).
  • 20. MacConville (2012).
  • 21. Stevenson (1973); Haraldsson (2012).
  • 22. See, for example, Bell (2008).
  • 23. Lawrence (2013).
  • 24. Pearson (2014).
  • 25. Alvarado (2014).
  • 26. Osis and Haraldsson (1971/2012).
  • 27. Barrett (1926; 2012).
  • 28. Greyson (2010), 159-71.
  • 29. Osis and Haraldsson (1971/2012).
  • 30. Singh (2000).
  • 31. Osis & Haraldsson (1971; 2012).
  • 32. Fenwick et al (2009); Brayne et al (2008), 195-206.
  • 33. Cook (2013).
  • 34. Geiger (2008).
  • 35. Geiger (2008).
  • 36. Steffen and Coyle (2012).
  • 37. Pearson (2014).
  • 38. Callanan and Kelly (1992).
  • 39. Lawrence (2013); Nosek (2015).
  • 40. Seguin (2009).
  • 41. Nahm et al (2012).
  • 42. Haig (2007).
  • 43. Nahm & Greyson(2013-2014), 77-87.
  • 44. IANDS, Greyson NDE Scale.
  • 45. Charland-Verville et al (2014)
  • 46. Charland-Verville et al (2014).
  • 47. Pearson (2014).
  • 48. See, for example, Franke (2014).
  • 49. Otto (1917/2012).
  • 50. Underhill (1919/1999).
  • 51. Zaleski, C. (1987).
  • 52. Blackmore, S. (1993).
  • 53. Nelson et al (2006), 1003-9.
  • 54. Lopez et al (2006).