Many users of dextromethorphan (DXM) report an effect on their visual perception of motion that is compared to everything being illuminated by a strong strobe light, with perceived gaps or pauses between each visual frame. A variety of terms are used to describe this effect, including "strobing", "flanging", "chopping", "lag", "clipping", "freeze-framing", "stop motion", "disturbances in motion", and "filmstripping". Unfortunately, most of those terms are also used to describe other effects like strong nystagmus, afterimages, trails, and memory gaps, and do not appear to have clearly unique meanings in DXM experience reports. Because of similarities in descriptions, the medical term "akinetopsia" (inability to visually perceive motion or "motion blindness") was recently proposed to refer to this effect, but the effect described by DXM users do not seem to qualify as an actual inability to perceive motion. We will use the phrase "stop motion effect" to refer to the effect that hundreds of DXM users describe: having movements in the visual field lag slightly behind normal perception in a staccato series of static images, some of which may persist and interfere with current vision.

William White's influential DXM FAQ primarily uses the term "flanging" to describe this effect:

The most general sensory effect of the second plateau is "flanging". Flanging, also called phlanging, phasing, stop-action, framing, strobing, etc., is the sensation that continuous sensory input has been chopped up into frames (as if you were watching a badly animated cartoon), often with some echo effect of each frame. There does not seem to be any loss of sensory content; instead, it is as if the ability to keep sensory input time-continuous were disturbed. The best analogy from other drugs may be the effects of nitrous oxide upon sound. The best analogy from non-drug experiences is listening to a voice through an echo/delay effects box (which is where the term "flanging" comes from).

[...] Vision suffers a curious change, seeming to consist of well-processed but highly strobed images; so strong is the effect that it seems as if one is looking at the world under a fast strobe light. The eyes don't seem to track in synch with the inner 3D model of the world, so that when one looks to one side or another, the world lurches back and forth for a moment. [ DXM FAQ ]

Unfortunately, the terms that are used to describe stop motion effects in DXM reports are also used to describe other related and unrelated effects. Because of this overlap, not every use of "strobing", "flanging", "chopping", etc. can be assumed to refer to this visual phenomenon. Each use of the term has to be parsed for context and it is often not clear exactly what the author is describing.

The DXM FAQ's use of the audio term "flanging" may create some confusion, as it could be understood to refer to visual noise around objects, blurring, halos, or possibly trail-like after images and may not distinctly denote stop motion effects. "Flanging" is also used to describe audio, visual, and time perception.

The terms "trails" and "tracers", frequently used to describe visual effects experienced under the influence of higher doses of DXM, share similar visual impressions with the stop motion effect, but can and do occur without the characteristic primary visual impression of seeing in a series of static frames. Trails/tracers do not always co-occur with the stop motion effect.

Effects on memory may also result in similar experiential effects and descriptions. At higher doses, DXM, Cannabis, MDMA, and other strong psychoactives can result in disruptions of short term memory. Some DXM users describe a rapid, repetitive forgetting of the immediate past ("How did I get here?", "Did I just pick that up?", "Where did that come from?") that may result in perceived gaps in motion. A clear example of the use of "flanging" to refer to memory effects: "I was experiencing heavy flanging, to the extent that I could go downstairs, eat something, and then come back upstairs to find that it felt as if I had never went downstairs in the first place." (Rivethea, exp69103)

Simple time dilation, where the passage of time appears to be slowed or accelerated, is sometimes also described as "strobing" which provides another confound when using that term to describe the stop motion effect.

Also, at high doses of DXM, physical movements of the body become less fluid ("robowalk") and some descriptions of the experience of attempts to walk or move limbs are described using visual terms.

Nystagmus (involuntary eye jumping) caused by DXM can result in a variety of visual effects, some of which are described similarly to the stop motion effect. Visual stuttering, choppiness, and blurring are common with strong nystagmus, but in combination with other visual effects can cause complex patterns and after images.

Because most of the simple terms for the stop motion effect are not precise, some have suggested using the medical term "akinetopsia".(Anonymous 2009) Zeki (1991) defines akinetopsia as: "[...] a syndrome in which a patient loses specifically the ability to perceive visual motion following cortical lesions outside the striate cortex." (Zeki 1991). A short video about the first woman diagnosed with akinetopsia by Lola Kalman provides some examples of the types of effects that are defined to be part of the condition. In a 1999 paper, Horton and Trobe repurpose the term akinetopsia to refer to transient visual effects suffered by two patients receiving nefazodone, but do not perform tests on the case studies and simply collect experiential descriptions. (Horton 1999)

The primary problem with using "akinetopsia" to refer to the stop motion effect is that what most people describe is not unambiguously the inability to perceive and process objects in motion in the visual field. Most often, the effect is described in terms that suggest that there is the visual impression of stopped frames without descriptions of dysfunctions that would define an actual inability to perceive motion visually.

A secondary problem is that people may misunderstand the use of "akinetopsia" to suggest the effect is the result of brain damage, since the medical term is primarily used to describe an effect that is the result of damage to certain areas of the brain. There is no evidence that the DXM stop motion effect has anything to do with damage to the brain.

While the evidence is not yet clear that high doses of DXM result in verifiable motion blindness, there is substantial evidence of a distinct visual phenomenon with effects similar to akinetopsia. Research is necessary to evaluate the stop motion effect and determine whether it causes an actual inability to perceive motion. For now, it seems inappropriate to refer to the stop motion effect as akinetopsia, despite its allure.

The following are a set of quotes from first-hand experience reports that use a variety of terms to describe the stop motion effect. While not exhaustive, these are representative of the current frequency with which the terms have been used in reports submitted to Erowid as of May 2009. The Experience Vaults contain a total of 79,000 submitted reports, with 6700 reports including the strings "DXM" or "Dextrometho" in the submitted substance field.

Only descriptions of visual effects are included in the following examples. A few examples that were identified as clearly not referring to the stop motion effect are included under separate headings. Not all reports included here have yet been reviewed and published (perhaps you'd like to volunteer to help triage these reports?)

• Strobing
• Flanging (Describing stop motion effect)
• Flanging (Not describing stop motion effect)
• Frames
• Choppiness / Chopping (Describing stop motion effect)
• Choppiness / Chopping (Not describing stop motion effect)
• Freeze / Freezing
• Lag
• Stop Motion
• Slide Show (Describing stop motion effect)
• Slide Show (Not describing stop motion effect)
• Snap Shots

Related Terms

• Tracers : Over 120 reports submitted to the Experience Vaults (reviewed and unreviewed) included the term "tracer", but the term is rarely used to unambiguosly refer to the stop motion effect. We consider it to be a separate visual effect.
• Trails : A number of reports use the term "trails" to describe visual effects, but none use it to unambiguously refer to the stop motion effect without resorting to other descriptive terms.