The discussion begins with the presentation of our main findings, and then follows a presentation of how these findings are interpreted, in relation to theories mainly within environmental psychology.
4.1. Main Findings
Our overall aim was to study if FOG-reactions are triggered in natural environments. We were interested in the FOG reaction throughout the whole experiment and especially when passing through openings. This was done to study how FOG reactions develop in an experimental setting.
One finding was that not one subject had a FOG reaction when they passed through the hedge opening, even though they all reacted when they walked through doorways inside buildings. The hedge opening was as wide as a normal doorway. Next, a built element in form of a doorframe was added into the hedge openings. No other changes were made. All subjects reported self-estimated FOG-reactions throughout the trial. Two subjects had clear FOG reactions in the opening when the doorframe had been added to the hedge opening. This was proved, both by a strong measurable impact in the instruments, and by manifest observable expressions. For one subject, we found a slight deviation in the instruments. These three subjects also reported self-rated FOG in the hedge opening with a white doorframe.
For subjects one and two, further tests were carried out. The tests showed that subject one and subject two differed noticeably. Subject number one had a clear FOG reaction. One could observe a more labored gait with him. He pulled up his shoulders and modified the landing of one foot. Subject number two had a general FOG reaction of 6.6 throughout the experiment with the doorframe, but only 1.6 when he passed through the hedge opening without a doorframe.
When the test subject wore a cylinder which limited his peripheral visual field—i.e.
, when the person had limited capacity to visually fully interpret his environment [6
], FOG reactions were triggered even when the subject passed through green hedge openings. During no other test occasion did any of the subjects have any FOG reaction when passing through hedge openings without the doorframe.
An unexpected but clear finding was that all subjects describe strategies they use to reduce the impact of FOG in everyday life. The observations confirm that some of the subjects used strategies to prevent/avoid FOG reactions and locking. Subjects 1 and 4 did not use any visible strategy during the experiment. Subject number two walked with an unchanged pace through all the tests. By observing, we could see that the subject used clear marching-steps to avoid locking. Subject number three was skipping along in the experiment setting, also with an unnatural gait. Subject number four told us of a type of a dancing walk he used when he experienced FOG reactions and lockups. He also sought to prevent FOG by using the strategy of shutting his eyes before and during the passage; nonetheless, he had a clear FOG reaction.
Subject number five estimated his experience of FOG as very strong when passing through the doorframe, but used a deliberate strategy of increasing his walking pace and thus affecting or delaying FOG reactions from being triggered. He has found ways to make his way forward by strategically choosing a different kind of gait to his normal gait. It is more like dancing or marching than walking, techniques that many people use to delay the onset of locking. He says he can experience FOG reactions at any time and has probably experienced a need to move forward in this way. He also succeeds in making his way through all openings without apparent problems. However, based on his self-assessments, this required a lot from him both mentally and physically. He needed to put a lot of effort and concentration to partly counteract his natural walking pattern.
Subject number one had a kind of walk which appeared to be his usual walking pattern. He did not try to counteract this walking pattern, and instead he had the strongest FOG reaction. Could it be that when he walked without trying to subdue or prevent a FOG reaction, his gait established an unconscious communication with the surrounding environment; a communication which, among other things, has to do with avoiding dangers of various kinds [59
What is clear is that the two who did not show any measurable effects from the accelerometer when walking through the doorframe, had no visible reactions from the waist down. The strategies they used were focused on their legs. Both, conducting the experiment without measurable results from the accelerometer, had a non-natural type of gait throughout the study. Such strategies were not mentioned in the study by Almeida and Lebold [11
An additional finding must be highlighted: three of the subjects had a significant physical impact when they were low-medicated, which they also expressed in their interviews. This impact may lead to a perception of low motion control and may also cause concern for the individual: An inner awareness of an inability to cope with the situation physically may easily trigger a protective, survival reflex.
The clinical picture of Parkinson’s disease includes an array of common basic problems, but PD can manifest itself in different ways. The results of this study show that Parkinson’s symptoms and their physical and mental consequences are unique [6
]. They vary depending on, for example, medication and stress levels [6
]. Subjects described their experience of their illness and their individual experiences of cognitive and physical impact on low levels of medication. Some felt that the physical consequences were most apparent while others described psychological influences and effects as being the most dominant (see Table 1
). There were also various ways individuals tried to prevent or regain control from a FOG reaction by, for example, marching, dancing, crawling, hopping using a walker, or changing their stride and step speed [60
FOG has been interpreted as motor blockings, but recent research suggests that other factors may contribute. FOG has been shown to be associated with anxiety, depression, stress, and pain [4
]. In interviews, some of the relatives expressed surprise that their family member did not have any FOG reaction or lockings when passing through the doorframe. They reflected on reasons why. For instance, one relative said that if the subject experiences something as fun; it has a clear positive impact, and reduces his FOG reactions. Another family member mentioned that the expectations of the results of the tests could reduce the subject’s propensity for FOG and may be a factor affecting the test results [6
]. This can also happen during a doctor’s visit, when trying to but failing to trigger and exhibit a FOG reaction.
A doorframe in a hedge opening is not natural. It is an unnatural element in the outdoor environment. Three of the subjects had FOG reactions when passing through the doorframe—The visual information of the external, more natural environment, did not fit (straight lines and right angles) [6
]. The subjects’ reactions were different, depending on whether the subjects were able to use a strategy to avoid locking or not. One may suspect that the visual experience of the doorframe triggered the FOG reactions. In all experiments where the signals from the environment were either difficult to interpret (doorframe) or where there were no signals of a safe environment (cylinder), a FOG reaction was triggered. Lacking a full overview of the environment and thus not being able to interpret it [38
] may cause a hazard response [63
]. A frequently used technique in horror films is the limiting of that the visual field of view. Appleton’s prospect/refuge theory [64
] involves an overview of the place evoking safety and security. In addition, subject number two estimated big differences in his experience of general FOG in test rounds without doorframes compared with test rounds when passing through a doorframe (see Table 3
). Could this difference in estimation of general FOG be an expression of that the constructed element—This doorframe—Affecting the interpretation of the environment: A “danger” signal is roused? From a survival standpoint, it is considered to better to hit the brakes once too often than once in a while [65
4.2. Discussion, Related to Mechanisms of Information and Action
Decision making and action depend on us properly understanding and interpreting the information we take in. It is about paying attention to our surroundings, making decisions, and then acting. Attention Restoration Theory [37
] argues that we have two types of attention, directed attention and involuntary attention. There are two ways for the brain to take in information: Bottom-up, when information comes to us from the environment and is then processed, and top-down, where one is willfully looking for information [68
]. Directed attention is more about searching for information top-down, while involuntary attention is more about finding information bottom-up. Kaplan & Berman [68
] develop ART by claiming that most activities are dependent on both involuntary attention and directed attention. A task that is initially more to be considered as using directed attention can—The more used you become to the activity, through practice—switches to an automated behavior and thus uses the more involuntary attention in its implementation. For example, when training, a high jumper works on automating processes. The strategies many of the subjects in this study demonstrated may be because they have practiced “unnatural” gait behaviors that do work, hence, they automatically fall back on them.
] suggests that an individual’s decision making and action assumes that a solution is quick and easy (System 1). What usually works, but can sometimes lead to wrong conclusions. We also have a slow, reflective system (System 2), which we rarely use. Partly because System 2 is very slow, but also because it is very tiring to use. This can be interpreted as System 1 mainly using involuntary attention. System 2 can be interpreted as a special case of directed attention—An extreme directed attention, where nothing is based on routine or experience. Therefore, the subjects who practiced strategies in our study can make extensive use of System 1. Those who suddenly suffered from FOG and severe lockings tried to get out of this, maybe by using directed attention and System 2 in their decision-making, and therefore became greatly fatigued. We would like to discuss System 0, where decision-making is a pure reflex.
Work on nonhuman primates has shown that top-down attention is driven more by Pre-Frontal Cortex (PFC), whereas bottom-up attention is driven more by the Parietal-Temporal-Occipital region (PTO) [70
]. The PTO area consists of an association-area of the cerebral cortex, where skin-muscle-joint-sensations along with visual and auditory information are coordinated as an “inside view”: It is a 3-dimensional map which “shows the brain” partly how the world is constructed on the basis of visual and auditory stimuli, and partly the body’s position and movement in this environment; this is particularly based on information from muscle- and tendon organs and from the joint capsules [70
]. People with PD have trouble interpreting information from their body. They are more dependent on visual information than people normally tend to be, and are more reliant on peripheral visual feedback [71
] and on impressions without ambiguity—Otherwise a need for focused attention occurs [38
When peripheral vision was limited using a paper cylinder in the tests, it created a feeling of insecurity. The first FOG reaction occurred when passing through the hedge opening without the doorframe and with the cylinder. A clear “no danger” signal seems to be needed in order not to trigger a FOG reaction.
When one’s surroundings convey sensory input that signals “no danger”, this can contribute to the absence of FOG, like when passing through the hedge opening without the frame. Compared to an opening with a doorframe, a green hedge opening may also put less of a load on a person who always uses a technique to avoid FOG, as can be seen from subject number five, who experienced high self-rated FOG when he passed the doorframe in a hedge opening. Can built elements (straight, square, “non-natural”) trigger a “danger” reaction in us? A congenital ability in small children to avoid precipices on a surface consisting completely of straight lines and right angles has been demonstrated [72
]. Is the FOG reaction triggered when the white doorframe was encountered analogous with this?
Although all subjects experienced FOG-reactions at home and in the 360 degree test before the trials, they experienced no FOG-reactions in their gait cycle during tests in the more “natural” environment without any built element. This can be interpreted as an influence of a natural outdoor environment inhibiting or not triggering a FOG reaction. Neuroscience describes how human behavior is generated by information processing, consciously and unconsciously, with a focus on managing life and, in this, mixing the present with memories. There are descriptions of how we continuously interpret and make not yet made conscious decisions in an on-going stream of impressions, from both internal and external stimuli [73
]. This co-activation creates predictions of what is highly likely to be relevant in a specific situation. Our hypothesis is that what we see in this study are two different unconscious “predictions”: “danger” and “no danger”.
Perceiving certain animals (e.g., snakes and spiders), the sight of blood, heights, and darkness can quickly and unconsciously trigger a danger reaction in us [74
]. The physical environment itself may also trigger similar reactions of anxiety and fear, as well as security and safety [31
]. Several researchers describe the necessity of a non-threatening natural environment in order to lower individual people’s levels of stress [31
]. The biophilia hypothesis supports these findings. The hypothesis suggests that human responses to the natural environment in its simplest form are about “love of life and living systems”: Attraction or a philic reaction. Unlike phobias; philias are about the positive feelings people have toward certain environments, activities and objects in their natural milieus [77
]. An environment can signal a calm, positive, warm, interesting, and secure atmosphere, or the opposite—An insecure, threatening, and distressing atmosphere. These signals create communication [59
] and a flow of emotional tones [79
]. These tones can signal “danger” or “no danger”. This affects the prediction and the action. The emotional tone is a prelinguistic language, talking through our affects [59
When surroundings are experienced as ominous or threatening, the “danger response” will be promptly switched on, triggering freezing: A reaction which, in its purest form, is about survival [74
]. An “avoidance” reaction (flight or freeze) can take place without us consciously “seeing” the dangerous situation [80
]. We assume this could be what we find in our Parkinson’s patients with FOG: A chain of simulated stimuli and responses that are activated, resulting in freezing, an avoidance reaction. When stressed, the individual relies more on affects [36
]. Parkinson’s patients may possibly have a weakened ability to inhibit strong danger-reactions that may occur when passing through doorways. Visual impressions from nature signaling “no danger” have the ability to rapidly reduce stress via our affects [36
], which may be crucial to persons with PD and FOG. Is FOG an oversensitive, unconscious avoidance reaction?
What happens when the body freezes? The eyes capture something (bottom-up). It is processed in the brain and communicated to different systems. Öhman [74
] speaks of four main categories of phobia, those to do with animals (snakes, spiders), social phobias, phobias of injury and blood, and spatial phobias (steep precipices, open spaces and confined spaces). We suggest that what is happening regarding FOG may have to do with spatial phobias. Our evolutionary history is obvious in the fears and phobias that we humans exhibit and readily learn. We are more likely to fear events and situations that were threats to the survival of our predecessors, such as potentially deadly predators, wide-open spaces and heights, than to fear the most commonly encountered potentially deadly objects in our modern environment, such as firearms or motorbikes [81
Clearly, false negatives (that is, failing to bring about a defense to a potentially lethal stimulus) are more evolutionarily costly than false positives (that is, bringing about the response to a stimulus that in effect is risk-free). Thus, from an evolutionary perspective, it is likely that perceptual systems are biased toward discovering threat. To guarantee an effective defense when life is at stake, the system is biased to “playing it safe” by sometimes initiating a defense to something which, on closer examination, turns out to be harmless. Researchers like LeDoux [83
] explain the freezing-response as an instinctive action that is carried out in the service of protecting an animal or human being. In our theory, freezing is a response that automatically occurs without cognitive evaluation or planning. From an evolutionary point of view, freezing, in a context of spatial phobia, is an absolutely correct reaction, so a person, e.g., does not fall off a cliff. Freezing may occur because the incoming stimulus has triggered an intense response reaction that momentarily inhibits access to any thinking and planning. Yet, as the intensity of the physiological response declines, access to planning and thinking can be reinstated.
Usually when a visual stimulus is detected in the environment, a signal goes to the thalamus, and then to the sensory cortex (the high road) where it is interpreted. But if the stimulus is interpreted as extra hazardous, signals are sent directly to the amygdala (the low road). From the amygdala, signals that can trigger a freeze reaction are sent to the midbrain. It is described as a “quick and dirty” transmission route. It “probably does not tell the amygdala much about the stimulus, certainly not much about Gestalt or object properties of the stimulus, but it at least informs the amygdala that the sensory receptors of a given modality have been activated and that a significant stimulus may be present” [84
], so that the amygdala can start early activation of defense responses. This system is explicitly adopted to be adaptively biased toward false positives rather than false negatives. This is because it is less costly to abort falsely initialized defense responses than to fail to produce a defense when the threat is real [74