Human beings are semiotic entities. We largely live in and react emotionally to semiotics. Virtually everything we think, feel, and believe is built on a foundation of signs and symbols—semiotics.
A recent German study elegantly shows that people with arachnophobia see spiders more quickly than people who do not fear spiders.
The study can be found here: You See What You Fear: Spiders Gain Preferential Access to Conscious Perception in Spider-Phobic Patients. An article about the study is here: Phobias alter perception, German researchers say.
The authors of the study say that there probably is “an evolutionary advantage to preferentially process threatening stimuli, but these effects seem to have become dysfunctional in phobic patients.”
I would argue that “these effects” have also migrated into human semiotics and are similarly dysfunctional. That is, humans perceive some signs and symbols as more threatening than they are. For some of us these signs and symbols can seem so threatening we become “phobic” or neurotic about them.
For example, insecure people may become hypersensitive to signs of rejection. People who have been abused or tortured may perceive signs that seem ordinary to others as serious threats. If the person who tortures you also smiles, you will probably see human smiles as being dangerous when to others they indicate kindness.
Once a semiotic becomes associated with strong emotions, and this can happen in many ways, we will tend to see that semiotic as an emotionally charged sign from then on.
FIML practice is designed to interrupt our emotionally-charged responses to semiotics the moment those responses occur. By doing this repeatedly with the same sign, FIML practice can extirpates the neurotic response to that sign.
Edit: Extirpating semiotic “phobias” or neuroses should be easier to do in most cases than extirpating phobias based on visual perceptions of things, such as the spiders discussed in the linked study. This is likely due to the more direct connection between emotional or limbic responses and the visual cortex. Complex semiotics are signs and symbols built on top of other signs and symbols, and thus their “architecture” is more fragile than direct visual perception and probably simpler to change in most cases. Human facial expressions probably fall somewhere between complex signs and direct visual perception. A good deal of what we call “psychology” are networks of complex semiotics. When a network becomes “neurotic” it is probably true that it contains erroneous interpretations of some or all of its semiotics. That said, a complex neurosis than involves many semiotic networks may be more difficult to extirpate than a straightforward phobia like arachnophobia.