5 May 2014

Heywood & Zihl (1999) Case Study of L.M.’s Inability to Perceive Motion, in their book chapter “Motion Blindness”, summary notes

Corry Shores
[Search Blog Here. Index-tags are found on the bottom of the left column.]

[Central Entry Directory]

[Neuro-Science, entry directory]

Heywood and Zihl

“Motion Blindness”

Brief Summary:

L.M. is a woman who suffered a rare case of brain damage that resulted in her being unable to detect motion. She could see the different positions of moving objects but not the motion between them. Motion in place, like the stream of pouring water, seemed “frozen like a glacier”. I appeal to this case for the phenomenological argument that motion, change, and time itself are differential phenomenon: the phenomenal content is not just the different positions of a moving object, for example, but as well, the difference between them is itself phenomenal content. In other words, time and change phenomenologically speaking are differences and not objects or processes.


Neurophysiological studies indicate that our vision system has highly specialized parts.

The discovery of an impressive patchwork of cortical visual areas that lies in the extrastriate cortex of the monkey has led to the suggestion that each is relatively specialised for the processing of a particular visual attribute.

Thus, “the destruction of a single area will result in the disturbance of a single function.” [2a] But there are problems with this view. For example, already we have discovered 30 or so areas of  the macaque monkey brain used for vision, but there are not that many visual attributes which each one might specialize in. Also, there is no good way to make such a correlation [as the are regional variations which complicate such an analysis]. The second problem is that we have only identified a small  number of selective disorders [and so we cannot identify all the possible regions], and thirdly, “surgical removal of a single visual area in the monkey has rarely, if ever, resulted in a deficit that parallels any of the clinical findings.” [2]

Nonetheless, we still have cases of selective disorders that are useful to our scientific investigation into the brain’s visual areas.

There is a particularly important part of the brain for vision (found in the monkey brain). It is the cortical area V5, also known as MT. Research on this area indicated that the visual cortex of monkey brains has highly specialized parts. Regarding this V5 region of the visual cortex, “Neurons in this region are finely tuned to the direction of visual motion and it was promptly referred to as ‘the motion area.’” [2d] And shortly after this discovery there was a case study of a patient (L.M.) “with a relatively selective and profound deficit in the perception of visual motion […] (Zihl, von Cramon, & Mai, 1983)”. [3a]

The Case of L.M.

Patient L.M. had a brain injury that seemed to have disabled her ability to perceive motion (the injury occurred 1978, studies on her case began 1980, and Zihl et al. publish their report 1983). She could see the positions of mobile things but never the movements between those positions.

L.M. reported that looking at objects in motion made her feel quite unwell. The explanation she gave sounded rather odd. She claimed that she no longer saw movement; objects which should move, as she well remembered, now appeared as "restless" or “jumping around". Although she could see objects at different locations and distances, she was unable to find out what happened to them between these locations. She was sure that objects did not move, but appeared as "jumping from one position to the next, but nothing is in between''. Because of' these difficulties she avoided streets, busy places, supermarkets and cafés. Traffic had become very frightening; she could still identify cars without any difficulty but could not tell whether they were moving or stationary. The only w:ay for her to establish this was to wait until the car became either conspicuously bigger or small. However, this turned out to be very complicated, especially when there were other cars in the vicinity. As a consequence, she no longer risked crossing the street except at pedestrian crossings. When people walked nearby, she usually waited until they passed, because the ''restlessness"' they produced by their walking irritated her so much that she had to interrupt her walking to find a "resting point for my eyes". Furthermore, she reported substantial difficulty in pouring fluids into a cup or glass, because the tea, coffee or orange juice appeared "frozen like a glacier'. She could not see the fluid rising, and therefore, couldn't establish when to stop pouring. In addition, she felt very irritated when looking at people while they were speaking: their lips appear to ''hop up and down", so she had to look away so as not to become confused. "'To my friends, this behavior appears very strange if not unkind; they believe that I am no longer interested in their conversation because I am always looking absent-minded. But it is the only way to listen to them without being disturbed". For this reason she had decided no longer to meet her friends.

Behavior Consequences of L.M.’ Movement Vision Disorder

In this section L.M. is quoted as saying:

“Sometimes I do not even know whether a person is approaching me or is receding.”

Neuropsychological Assessment

In this section we learn that since L.M.’s case, there have been a number of other reported cases of deficits in motion perception. However, L.M. is still the case most extensively studied. Her condition has been coined akinetopsia by Zeki (1991)

Cerebral Akinetopsia

There is an effective test for the brain’s motion systems called ‘random dot cinematograms.’

one very effective way of establishing the capacity of the motion system is by testing with a class of visual stimuli known as random dot cinematograms. These are composed of a random display of elements which lack an overall conspicuous form. When some of the dots are spatially displaced during sequential frames of the display, the normal observer effortlessly perceives smooth visual motion. By varying the parameters of the display, such as the density, distributions of direction and distance of the displaced elements, exposure duration and interstimulus interval, the limits of motion vision can be characterised. The displays have the particular advantage that the observer is unable to determine which element in the second exposure corresponds to which element in the second [sic?]. It is therefore impossible to infer the motion from the change in location of individual elements. Processes that extract such motion have been termed “short-range” (Braddick, 1974), in contrast to longer-range processes that extract motion information from displays that contain small numbers of clearly defined elements.


[“Random Dot Kinematogram” animated gif from wikimedia commons]

Using this test, it was determined that at certain levels of variation, L.M. could not perceive motion.

Besides being unable to detect motion at a certain level, she was also unable to discriminate other properties of motion such as direction or velocity also at a certain level. “Even at low velocities, L.M. required a twenty-fold increase in contrast, compared with the normal observer, to correctly judge the direction of motion.” [9a] However with other testing it was determined that her deficit was not “in the direction of motion but in making judgments of the attributes of stimulus motion.” [9a]

Heywood, C. A., & Zihl, J. (1999). Motion blindness. In G. W. Humphreys  (Ed.), Case Studies in the Neuropsychology of Vision (pp. 1-16). Hove: Psychology Press.
Summary based on limited preview at google books:

Random Dot Kinematogram animated gif from:
Wikipedia commons
Random Dot Kinematogram (Elliptical).gif

No comments:

Post a Comment