Stephen F. Austin State University
April 29, 2002
Visual agnosia is a neurological disorderdistinguished by the inability to recognize familiar objects. Mostcases of visual agnosia are brought about through cerebral vascularaccidents or traumatic brain injury, typically inhibiting sufficientamounts of oxygen from reaching vital body tissues (Farah, 1990).There are a vast array of impaired abilities and deficits associatedwith individuals diagnosed with visual agnosia. These impairmentsvary considerably from individual to individual (Farah, 1999). Somepatients cannot recognize pictures of things such as trees and birds,despite being able to describe such objects or recognize them throughother senses such as sound and touch. Other patients demonstrate aninability to recognize faces of friends and family members (Farah,1990). Furthermore, some agnosic individuals cannot copy familiarobjects in simple drawings. The functional impairments experienced asa result of visual agnosia are detrimental to both the diagnosedindividual and all those who interact with the individual.
Unfortunately, object recognition disorders suchas agnosia comprise a neglected field of study, and the existingtheories to explain this phenomenon are often vague and problematic(Farah, Monheit, & Wallace, 1991). Visual agnosia is a very raresyndrome and there is only a small number of cases available tostudy. This research obstacle is further compounded by the varianceof impairments in visual agnosics (Vecera & Gilds 1998). In anattempt to group similar cases of visual agnosia for more sufficientstudy, two separate categories have emerged. Apperceptive agnosia istypically characterized by an inability to recognize familiar objectscaused by damage to early perceptual processes and associativeagnosia is typically characterized by an inability to recognizefamiliar objects despite having no damage to early perceptualprocesses (Vecera & Gilds 1998). However, the different fields ofstudy and various researchers involved in studying visual agnosiaoften have discrepancies in defining these categories.
The most recent explanation for the visualimpairments experienced by visual agnosics is the peppery maskaccount. It is theorized that patients with visual agnosia have apresence of random visual noise as a result of obstructing airbubbles circulating in the blood or from blood clots present in anintact blood vessel (Farah et al. 1991). Because of obstruction,random areas of dimmed vision are scattered throughout the visualfield in varying size and severity; thus the visual agnosic sees theworld through a peppered mask that degrades their visual processing.In an experiment by Vecera & Gilds (1998), researchers covereddifferent displays with a peppery mask to simulate the peppery maskcondition in subjects with normal vision (Farah 1999). Normalsubjects were expected to simulate the behavior of a visual agnosicpatient when looking through the manipulated mask. However, themanipulation of a peppery mask did not exhibit different patterns ofbehavior from the patterns of behavior measured from unmaskeddisplays (Vecera & Gilds, 1998). While the peppery mask accountexplains the degraded low-level visual processing, the theory offersno explanation for the various grouping disorders that tend to appearin visual agnosics.
In an effort to seek understanding and explanationof perceptual grouping disorders researchers formulated thegrouping-deficit account. This account hypothesizes that patientswith visual agnosia have impairments in preattentive perceptualgrouping process (Vecera & Gilds 1998). Such impairments wouldinclude difficulty in organizing segments of information into thetotality of the information it represents. The main limitationimposed on the grouping-deficit account is that little data existsfrom patients that examines lower-level grouping processes (Farah1999). An experiment was conducted to explore the grouping-deficitaccount. Vecera & Gilds (1998) removed nonaccidental propertiesfrom displayed objects, such as parallelism and cotermination, andvarious aids used to organize or group the visual field. When theseproperties were removed object recognition and grouping was difficultin normal subjects, if not impossible (Vecera & Gilds 1998).
Currently, researchers are taking new approachesin determining which account of visual agnosia best explains thesyndrome. Through experimentation, researchers have been attemptingto simulate visual agnosia in subjects with normal vision in order tomove beyond individual case studies with agnosia patients. Given thevast differences of impairments between patients with visual agnosia,the lack of clarity in defining categories of visual agnosia, and thefailure to formulate a proficient explanation of the cognitivemechanisms behind the hidden perceptual processes that are involvedin the syndrome of visual agnosia, it can be concluded that furtherresearch is desperately needed. Nevertheless, experiments such as thepeppery mask experiments and the grouping-deficit account yieldsignificant pieces of a puzzle that show encouraging signs of fittingtogether to enhance our understanding and advancement of knowledgesurrounding object recognition disorders.
Further compounding the difficulty of defining andunderstanding agnosia is the proposal of similar impairments presentin patients with the same hemisphere of the brain damaged (Humphreys,1999). Agnosia has been diagnosed in patients with varying types ofbrain damage. Cases have been noted after both unilateral andbilateral damage to both right and left hemispheres of the brain(Humphreys, 1999). According to Humphreys (1999), left hemispherepatients are typically marked by the inability to copy objects insimple drawings presented in most forms of presentation.Additionally, right hemisphere patients are better are copyingobjects from real objects presentations when they are allowed tointeract with objects and use the senses of touch. Patients withright hemisphere lesions are typically marked by an ability to betterrecognize and label objects when grouping cues such as color arepresent while left hemisphere patients are typically can labelobjects with and without color present. However, left hemispherepatients faced with labeling tasks generally show the same labelingability with or without color cues (Humphreys, 1999).
The proposed research is intended to bringtogether a large group of individuals diagnosed with visual agnosia.By focusing research on a large group of agnosia patients instead ofusing individual case studies or attempting to simulate agnosia innormal subjects, the impairments and deficits can be furtherexplored. There is a need for clear definitions and classificationsof visual agnosia in order to advance current research on agnosics.It is proposed that a better understanding and definition ofclassifications of agnosia can be achieved by conducting objectrecognition research on a group of agnosic individuals with righthemisphere damage and a group of individuals with left hemispheredamage. Differences between right and left hemisphere patients can bedetermined and similarities across all visual agnosics can beexplored as well. It is hypothesized that different presentationforms of familiar objects will influence the ability to recognizeobjects and the ability to copy them in drawings with a significantinteraction among individuals with right and left hemispheredamage.
Participants will be individuals diagnosed withvisual agnosia randomly selected from a compilation of visual agnosiapatients in the United States. A total of 20 individuals will berandomly selected from all visual agnosia patients who respond to aninvitation to participate. The total of 20 individuals will include10 individuals marked by a left hemisphere lesion and 10 individualsmarked by a right hemisphere lesion.
A university laboratory will be used to conductexperiments. Twenty familiar objects will be selected from theobjects used in research conducted by Stone, Buckley, & Moger(2000) will be collected. For a list of objects selected see table1.8. Real objects will serve as color 3D presentations. Each objectwill be processed into a colorless ceramic mold to serve as colorless3D presentations. Furthermore, each object will be photographed onboth color and black-and-white film, and developed into 10x10 photosto serve as color and colorless 2D presentations. Each participantwill be provided with a drawing pad, pencil, and eraser to performobject copying tasks. Additionally, experimenters will be providedwith scoring sheets to rank the level of object identification andthe level of copying ability. Each participant will also be providedwith a set of experiment instructions, and a copy of the consent formand debriefing form.
The experiment proposed is a 4 x 2 within subjectsdesign with the variables Type of Presentation (real object, ceramicmold, color photo, black and white photo) and Type of Brain Lesion(right, left). The two dependent variables proposed are the givenranks on the prescribed scale of one to three given for the objectlabeling task and the rank on the prescribed scale of one to threegiven for the object copying task. It is hypothesized that differentpresentations of familiar objects will influence the ability torecognize objects and the ability to copy them in drawings with asignificant interaction among individuals with right and lefthemisphere damage. Right hemisphere patients are hypothesized toperform poorly on object labeling tasks when color cues are notpresent while left hemisphere patients will show no significantdifference in labeling tasks with or without color cues. Furthermore,left hemisphere patients will perform poorly on object copying tasksin all forms of presentation while right hemisphere patients willperform better at copying tasks when color cues arepresent.
Participants will enter the university laboratoryand they will be given a copy of the consent form and experimentinstructions, as well as a drawing pad, pencil, and eraser. Theexperimenter will read and explain both the consent form andinstructions orally to participants and have them marked theirsignature on the consent form.
In order to prevent the systematic influence oftop-down processing on labeling and copying tasks, half of theparticipants are to be randomly assigned to label objects first andcopy objects second, while the other half of participants are to berandomly assigned to copy objects first and label objects second.Participants with right hemisphere lesion (R1 through R10) andparticipants with left hemisphere lesions (L1 through L10) will berandomly assigned to two groups. Group A will be asked to label theobject and then draw and group B will be asked to draw the object andthen label in order to prevent the systematic effect of top downprocessing.
Participants may be marked by learning and fatigueeffects as a result of being presented the same object in fourdifferent levels of presentation. To counterbalance this effect, the10 left hemisphere lesion patients and 10 right hemisphere patientsare to be randomly assigned to one of five prescribed orders ofpresentation levels. Participants L1 & L6 and R1& R6 will bepresented random familiar objects in presentation form order of realobject, ceramic mold, color photo, and black and white photo. Ps L2& L7 and R2 & R7 will be presented random familiar objects inpresentation form order of ceramic mold, color photo, black and whitephoto, and real object. Ps L3 & L8 and R3 & R8 will bepresented random familiar objects in presentations form order ofcolor photo, black and white photo, real object, and ceramic mold. PsL4 & L9 and R4 & R9 will be presented random familiar objectsin presentation form order of black and white photo, real object,ceramic mold, and color photo. Finally, Ps L5 & L10 and R5 &R10 will be presented random familiar objects in presentation formorder of color photo, real object, black and white photo, and ceramicmold.
Each time a participant is presented with afamiliar object in any form of presentation they will be allowed tointeract with the object through touch. According to Zemel, Behrmann,Mozer & Bavelier (2002), agnosia patients who are allowed tophysically attend to objects will exhibit a stronger ability torecognize objects. After Group A is presented with a familiar object,they will first be asked to label the object. Experimenters will rankthe subjects ability to label an object on a one to three scale witha rank of one indicating a completely incorrect label, a rank of twoindicating a correct category identified, and a rank of threeindicating a correct label. Group A will then be asked to draw theobject from its form of presentation and experimenters will then ranktheir ability to draw on a one to three scale. A rank of one willindicate a completely incomparable drawing, a rank of two willindicate a partially comparable drawing, and a rank of three willindicate a comparable drawing.
When members of Group B are presented with afamiliar object they will first be asked to draw the object from itsform of representation and then label the object and experimenterswill then rank them on the appropriate one to three scale.
After participants have been presented allpresentations of the twenty familiar objects the experimenter willread a debriefing form to participants and answer any questionsregarding the general nature of the experiment before being released.
In an experiment conducted by Zemel et al. (2002),ranking scores were generated from subjects in object labeling andcopying tasks. The data to be collected in this experiment will bethe labeling task and copying task ranking scores similar to theranking scales used by Zemel et al. (2002). Labeling task scores areto be submitted to a within subjects 4x2 factorial ANOVA. It ishypothesized that a significant interaction will be revealed. It isproposed that participants with left hemisphere lesions will performbetter than participants with right hemisphere lesions when objectpresentations are without color (ceramic molds and black and whitephotos) while participants with right hemisphere lesions will performbetter when objects presentations include color (real objects andcolor photos).
According to Humphreys (1999), patients with righthemisphere lesions are typically marked by an ability to betterrecognize and label objects when grouping cues such as color arepresent. Left hemisphere patients are typically show no differencesin labeling ability between objects with color cues and objectswithout color cues.
Secondly, copying task rankings are to besubmitted to a separate within subjects 4x2 factorial ANOVA. It ishypothesized that results of this analysis will reveal a significantinteraction with right hemisphere lesion participants performingbetter than left hemisphere lesion participants in all forms ofobject presentation. Furthermore, the analysis will reveal righthemisphere lesion participants performing significantly better atcopying from the presentation of real objects verses the otherpresentation types (Humphreys, 1999).
According to Humphreys (1999), left hemispherepatients are typically marked by the inability to copy objects insimple drawings presented in most forms of presentation. Furthermore,right hemisphere patients are better are copying objects from realobjects presentations when they are allowed to interact with objectsand use the senses of touch.
The results will support the hypothesis thatdifferent presentations of familiar objects will influence theability to recognize objects and the ability to copy them in drawingswith a significant interaction among individuals with right and lefthemisphere damage.
Agnosia patients with right hemisphere lesionswill perform better at labeling familiar objects when color ispresent. It is suggested by Humphreys (1999) that patients with righthemisphere lesions perform poorer at object recognition as theybecome increasingly removed from objects (from 3-D to 2-D and movingfrom color presentations to colorless presentations). Furthermore,agnosics with left hemisphere lesions will exhibit an inability tocopy objects from any form of presentation (Vecera & Gilds 1998).Additionally, right hemisphere agnosics will perform better atcopying familiar objects when they are allowed to interact with realobjects (Zemel et al. 2002). Right hemisphere patients generallyperform better at copying objects from real object presentations(Vecera & Gilds 1998).
The proposed experiment is intended to expand onthe current knowledge of the different various impairments presentbetween right and left hemisphere lesion agnosics. An experiment witha large group of individuals with visual agnosia would help toprovide clear definitions of subtypes of visual agnosia. A largegroup exhibiting similar impairments would be better equipped togeneralize subtype definitions to all individuals with agnosia asopposed to the current limited research on individual casestudies.
Furthermore, current research intended to focus onthe ability to learn to recognize objects is also limited by the lackof research on a large group of individuals with visual agnosia(Bischof, 2002). While researchers have been able to work with anindividual case studies in an effort to help them learn to recognizeobjects, not enough research on a large group of individuals has beendone and therefore the learning techniques are not able to begeneralized to all individuals with visual agnosia (Bishof, 2002). Bydetermining specific impairments characteristic of right and lefthemisphere patients, research can begin to focus on overcoming thesespecific obstacles. Additionally, pioneering work on the role ofobject appearance and its influence on object recognition is lackingin the ability to generalize a sample of agnosia patients to thepopulation of all agnosia patients (Appearance Based Approaches toObject Recognition).
In conclusion, some researchers share theviewpoint that research in the area of visual agnosia and objectrecognition will not only be applied to patients diagnosed withvisual agnosia, but also advance the overall understanding of visualagnosia (Visual Object Recognition). Given the vast differences ofimpairments between patients with visual agnosia, the lack of clarityin defining categories of visual agnosia, and the failure toformulate a proficient explanation of the cognitive mechanisms behindthe hidden perceptual processes that are involved in the syndrome ofvisual agnosia; it can be concluded that the proposed research is atype of research that would be a necessity to understanding visualagnosia.
Bischof, W.F. (2002) Learning to RecognizeObjects. Spatial Vision. 13 (2-3), 297-304.
Farah, M.J. Visual Agnosia: Disorders of ObjectRecognition and What They Tell Us About Normal Vision. The MitPress: Massachusettes, 1990. 155p.
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Zemel, R.S., Behrmann, M., Mozer, M.C. &Bavelier, D. (2002) Experience Dependent Perceptual Grouping andObject-Based Attention. Journal of Experimental Psychology: HumanPerception & Performance. 28 (1), 202-217.
Appearance Based Approaches to Object Recognition(n.d.) Retrieved March 3, 2002, from www.prip.tuwien.ac.at/Research/ObjectRecognition/
Visual Object Recognition (n.d) Retrieved March 3,2002, from http://cognet.mit.edu/MITECS/Entry/Farah2