a page out of a book. the patient will be unable to orient their eyes to the left margin and will begin reading the page from the center. presenting a single word to a patient will result in the patient either reading only the ipsilesional part of the word or replacing the part they cannot see with a logical substitute. for example, if they are presented with the word "peanut", they may read "nut" or say "walnut". varieties neglect is a heterogenous disorder that manifests itself radically differently in different patients. no single mechanism can account for these different manifestations. a vast array of impaired mechanisms are found in neglect. these mechanisms alone would not cause neglect. the complexity of attention alone—just one of several mechanisms that may interact—has generated multiple competing hypothetical explanations of neglect. so it is not surprising that it has proven difficult to assign particular presentations of neglect to specific neuroanatomical loci. despite such limitations, we may loosely describe unilateral neglect with four overlapping variables: type, range, axis, and orientation. type types of hemispatial neglect are broadly divided into disorders of input and disorders of output. the neglect of input, or "inattention", includes ignoring contralesional sights, sounds, smells, or tactile stimuli. surprisingly, this inattention can even apply to imagined stimuli. in what's termed "representational neglect", patients may ignore the left side of memories, dreams, and hallucinations. output neglect includes motor and pre-motor deficits. a patient with motor neglect does not use a contralesional limb despite the neuromuscular ability to do so. one with pre-motor neglect, or directional hypokinesia, can move unaffected limbs ably in ipsilateral space but have difficulty directing them into contralesional space. thus a patient with pre-motor neglect may struggle to grasp an object on the left side even when using the unaffected right arm. range hemispatial neglect can have a wide range in terms of what the patient neglects. the first range of neglect, commonly referred to as "egocentric" neglect, is found in patients who neglect their own body or personal space. these patients tend to neglect the opposite side of their lesion, based on the midline of the body, head, or retina. for example, in a gap detection test, subjects with egocentric hemispatial neglect on the right side often make errors on the far right side of the page, as they are neglecting the space in their right visual field. the next range of neglect is "allocentric" neglect, where individuals neglect either their peri-personal or extrapersonal space. peri-personal space refers to the space within the patient's normal reach, whereas extrapersonal space refers to the objects/environment beyond the body's current contact or reaching ability. patients with allocentric neglect tend to neglect the contralesional side of individual items, regardless of where they appear with respect to the viewer. for example, in the same gap detection test mentioned above, subjects with allocentric hemispatial neglect on the right side will make errors on all areas of the page, specifically neglecting the right side of each individual item. this differentiation is significant because the majority of assessment measures test only for neglect within the reaching, or peri-personal, range. but a patient who passes a standard paper-and-pencil test of neglect may nonetheless ignore a left arm or not notice distant objects on the left side of the room. in cases of somatoparaphrenia, which may be caused by personal neglect, patients deny ownership of contralesional limbs. sacks (1985) described a patient who fell out of bed after pushing out what he perceived to be the severed leg of a cadaver that the staff had hidden under his blanket. patients may say things like, "i don't know whose hand that is, but they'd better get my ring off!" or, "this is a fake arm someone put on me. i sent my daughter to find my real one." axis most tests for neglect look for rightward or leftward errors. but patients may also neglect stimuli on one side of a horizontal or radial axis. for example, when asked to circle all the stars on a printed page, they may locate targets on both the left and right sides of the page while ignoring those across the top or bottom. in a recent study, researchers asked patients with left neglect to project their midline with a neon bulb and found that they tended to point it straight ahead but position it rightward of their true midline. this shift may account for the success of therapeutic prism glasses, which shift left visual space toward the right. by shifting visual input, they seem to correct the mind's sense of midline. the result is not only the amelioration of visual neglect, but also of tactile, motor, and even representational neglect. orientation an important question in studies of neglect has been: "left of what?" that is to say, what frame of reference does a subject adopt when neglecting the left half of his or her visual, auditory, or tactile field? the answer has proven complex. it turns out that subjects may neglect objects to the left of their own midline (egocentric neglect) or may instead see all the objects in a room but neglect the left half of each individual object (allocentric neglect). these two broad categories may be further subdivided. patients with egocentric neglect may ignore the stimuli leftward of their trunks, their heads, or their retinae. those with allocentric neglect may neglect the true left of a presented object, or may first correct in their mind's eye a slanted or inverted object and then neglect the side then interpreted as being on the left. so, for example, if patients are presented with an upside-down photograph of a face, they may mentally flip the object right side up and then neglect the left side of the adjusted image. in another example, if patients are presented with a barbell, patients will more significantly neglect the left side of the barbell, as expected with right temporal lobe lesion. if the barbell is rotated such that the left side is now on the right side, patients will more significantly neglect the left side of the object, even though it is now on the right side of space. this also occurs with slanted or mirror-image presentations. a patient looking at a mirror image of a map of the world may neglect to see the western hemisphere despite their inverted placement onto the right side of the map. various neuropsychological research studies have considered the role of frame of reference in hemispatial neglect, offering new evidence to support both allocentric and egocentric neglect. to begin, one study conducted by dongyun li, hans-otto karnath, and christopher rorden examined whether allocentric neglect varies with egocentric position. this experimental design consisted of testing eleven right hemispheric stroke patients. five of these patients showed spatial neglect on their contralesional side, while the remaining six patients showed no spatial neglect. during the study, the patients were presented with two arrays of seven triangles. the first array ran from southwest to northeast (sw-ne) and the second array ran from southeast to northwest (se-nw). in a portion of the experimental trials, the middle triangle in the array contained a gap along one side. participants were tested on their ability to perceive the presence of this gap, and were instructed to press one response button if the gap was present and a second response button if the gap was absent. to test the neglect frame of reference, the two different arrays were carefully situated so that gap in the triangle fell on opposite sides of the allocentric field. in the sw-ne array, the gap in the triangle fell on the allocentric right of the object-centered axis along which the triangle pointed. in the se-nw configuration, the gap in the triangle fell on the allocentric left of the object-centered axis. furthermore, varying the position of the arrays with respect to the participant's trunk midline was used to test egocentric neglect. the arrays were therefore presented at 0° (i.e. in line with the participant's trunk midline), at −40° left, and at +40° right. ultimately, varying the position of the array within the testing visual field allowed for the simultaneous measurement of egocentric neglect and allocentric neglect. the results of this experimental design showed that the spatial neglect patients performed more poorly for the allocentric left side of the triangle, as well as for objects presented on the egocentric left side of the body. furthermore, the poor accuracy for detecting features of the object on the left side of the object's axis was more severe when the objects were presented on the contralesional side of the body. thus, these findings illustrate that both allocentric and egocentric biases are present simultaneously, and that egocentric information can influence the severity of allocentric neglect. a second study, conducted by moscovitch and behrmann, investigated the reference frame of neglect with respect to the somatosensory system. eleven patients with parietal lobe lesions and subsequent hemispatial neglect were analyzed during this experiment. a double simultaneous stimulation procedure was utilized, during which the patients were touched lightly and simultaneously on the left and right side of the wrist of one hand. the patients were tested both with their palms facing down and with their palms facing up. this experimental condition allowed the scientists to determine whether neglect in the somatosensory system occurs with respect to the sensory receptor surface (egocentric) or with respect to a higher-order spatial frame of reference (allocentric). the results of this experiment showed the hemispatial neglect patients neglected somatosensory stimuli on the contralesional side of space, regardless of hand orientation. these findings suggest that, within the somatosensory system, stimuli are neglected with respect to the allocentric, spatial frame of reference, in addition to an egocentric, sensory frame of reference. ultimately, the discoveries made by these experiments indicate that hemispatial neglect occurs with respect to multiple, simultaneously derived frames of reference, which dictate the nature and extent of neglect within the visual, auditory, and tactile fields. treatment treatment consists of finding ways to bring the patient's attention toward the left, usually done incrementally, by going just a few degrees past midline, and progressing from there. rehabilitation of neglect is often carried out by neuropsychologists, occupational therapists, speech-language pathologists, neurologic music therapists, physical therapists, optometrists, and orthoptists. forms of treatment that have been tested with variable reports of success include prismatic adaptation, where a prism lens is worn to pull the vision of the patient towards the left, constrained movement therapy where the "good" limb is constrained in a sling to encourage use of the contralesional limb. eye-patching has similarly been used, placing a patch over the "good" eye. pharmaceutical treatments have mostly focused on dopaminergic therapies such as bromocriptine, levodopa, and amphetamines, though these tests have had mixed results, helping in some cases and accentuating hemispatial neglect in others. caloric vestibular stimulation (cvs) has been shown to bring about a brief remission in some cases. however this technique has been known to elicit unpleasant side-effects such as nystagmus, vertigo and vomiting. a study done by schindler and colleagues examined the use of neck muscle vibration on the contralesional posterior neck muscles to induce diversion of gaze from the subjective straight ahead. subjects received 15 consecutive treatment sessions and were evaluated on different aspects of the neglect disorder including perception of midline, and scanning deficits. the study found that there is evidence that neck muscle stimulation may work, especially if combined with visual scanning techniques. the improvement was evident 2 months after the completion of treatment. other areas of emerging treatment options include the use of prisms, visual scanning training, mental imagery training, video feedback training, trunk rotation, galvanic vestibular stimulation (gvs), transcranial magnetic stimulation (tms) and transcranial direct-current stimulation (tdcs). of these emerging treatment options, the most studied intervention is prism adaptation and there is evidence of relatively long-term functional gains from comparatively short-term usage. however, all of these treatment interventions (particularly the stimulation techniques) are relatively new and randomised, controlled trial evidence is still limited. further research is mandatory in this field of research in order to provide more support in evidence-based practice. in a review article by pierce & buxbaum (2002), they concluded that the evidence for hemispheric activation approaches, which focuses on moving the limb on the side of the