Introduction
Research Group
Scope of Project
Using Visual Demonstrations
Psychophysical Experiments
Psychophysical Screens
Delayed Match-to-Sample Experiments
Visual Search Experiments
References
Visual Quick Tests
Related Links
 
 
 
 
 

Introduction

We have an ambitious goal: To understand, using rigorous psychophysical methods, the visual deficits that develop in Alzheimer's Dementia (AD). There have been several neuropsychological studies of visual deficits in AD [1-4], and some psychophysical studies [5-9]. These studies indicate deficits in color, contrast sensitivity, stereoacuity, optic flow, self motion, and object recognition.
 
 

Research Group

PI:   W. Rod Shankle
Co-I's:   Junko Hara, Ron Hirz, Donald D. Hoffman
Graduate Students:   Colleen Nilson, Tony Rodriguez
Pregraduate students:   Mayshen Chen, Joanne Christopherson, Tuyet Thi Dinh, Naeko Imagawa, Thoai Nguyen, Si Tran
 

Scope of Project

There are many aspects of vision in AD that need to be studied. A partial list follows:

1. Acuity
2. Spatial contrast sensitivity
3. Brightness
4. Color
5. Shading
6. Occluding contours
7. Texture
8. Perspective
9. Apparent motion
10. Optic flow
11. 3D structure from motion
12. 3D structure from static images
13. Stereovision
14. Subjective contours
15. Subjective surfaces
16. Amodal completion
17. Neon color spreading
18. Parts and part salience
19. Object recognition
20. Delayed recall of visual stimuli

Using Visual Demonstrations

The first approach is a shotgun approach, where we create minitests and simple visual demonstrations to show to AD patients. These can give us a quick idea of possible deficits, without time-consuming psychophysical tests. For instance, we have shown this figure to several AD patients:

While normals easily see the neon worm on the right, several AD patients do not. This suggests that neon color spreading is an interesting area to explore with detailed psychophysics. We have also shown this figure to AD patients:

Normals see a large apparent difference in size of the table tops, but some AD patients do not. This suggests that pictorial cues to depth is an interesting area to explore. We have shown this figure:

Normals see a subjective necker cube, but some AD patients do not. This suggests that subjective contours and amodal completion are interesting areas to explore. And we have shown this figure:

For normals, the heart in the box pops out, but some AD patients can't find the heart even with prolonged scrutiny. This suggests that parts and part salience are interesting areas to explore.

We now have more than a dozen figures like these to try out on AD patients, and we need to make many more. Some will be static and some will involve motion displays. Copies of the figures we have so far are appended to the end of this document.
 
 
 
 

Psychophysical Experiments

We will need to develop dozens of rigorous psychophysical experiments, many of which will be run on Superlab. The experiments must be specially designed for the needs of AD patients. In particular, they cannot be too long or too tedious. Yet they must give data adequate for statistical analysis.

Among the tasks we plan to use are (1) visual search and (2) delayed match-to-sample. Visual search tasks require the subject to find a target stimulus against a background of distractor stimuli. With normal subjects the accuracy in visual search tasks is near perfect, and the dependent variable of interest is reaction times. With AD patients we may find that accuracy is also an interesting dependent variable. Visual search tasks will allow us to check whether the processing of specific features has been impaired; subjects might not be able to process a feature at all, or they might process it serially/attentively when normals process it in parallel and preattentively. The delayed match-to-sample tasks require the subject to hold a specific visual stimulus in memory for a few seconds. These tasks will allow us to check whether the working memory for specific visual features has been impaired. Recent neural studies suggest that reciprocal connections between lateral prefrontal cortex and various sensory cortices are responsible for feature-specific working memories. These are often long-distance connections, and are likely to be among the first impaired in AD.

There are unique challenges in designing and interpreting psychophysical experiments for AD patients.  For example, if we obtain slower reaction times for AD patients on a certain psychophysical task, it may be that the AD patients are impaired on that visual function, or alternatively it may be that they are just generally slower at a certain class of tasks but not impaired on that visual function [10-12]. Performance may be impaired simply because AD patients may have trouble understanding instructions [13,14], or because they have limited attention or limited visual fields [15-17].
 
 
 

Psychophysical Screens

Before testing an AD patient for deficits in higher-level features, we must first determine that they have normal acuity, normal contrast sensitivity, and normal visual fields (no scotomas). We must also test that they are not protanopes, deuteranopes, or tritanopes. We will need to know if they are taking medicine for hypertension or other physical conditions. We will also need to know if they have had any strokes. All of these factors could alter the outcome of our psychophysical tests, and all must be taken into account.

Moreover, as required in our Human Subjects Protocol we must obtain written consent on Human Subjects Consent Forms for each subject tested. These forms will be available in SSL 393.

The psychophysical screens completed so far:

Naeko    - 11/16/99
Mayshen - 11/16/99a
Mayshen - 11/16/99b
 
 
 
 

Delayed Match-To-Sample Experiments
 

Experiment 1: Line orientation

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a line segment that is either horizontal, vertical, or oblique. The line segment remains on for 0.5 seconds. S tries to remember this line segment.
4. The screen goes blank for either 1, 2, or 4 seconds.
5. Two line segments appear side by side, the correct segment and a distractor.
6. S presses a button to indicate the correct line segment.

1. Independent variables: Line orientation (horizontal, vertical, oblique) and memory period (1, 2, 4 seconds). These variables are fully crossed, in a 3 x 3 design.
2. Dependent variable: Percent correct answers.
3. Repetitions of each condition: 10. This gives a total of 10 x 3 x 3 = 90 trials.
4. Counterbalancing: position of correct line segment and distractor
5. Counterbalancing: distractor line segments.

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a disk that is either red, green, blue, or yellow. The disk remains on for 0.5 seconds. S tries to remember this line segment.
4. The screen goes blank for either 1, 2, or 4 seconds.
5. Two disks appear side by side, the correct disk and a distractor.
6. S presses a button to indicate the correct disk.

1. Independent variables: Color (red, green, blue, yellow) and memory period (1, 2, 4 seconds). These variables are fully crossed, in a 4 x 3 design.
2. Dependent variable: Percent correct answers.
3. Repetitions of each condition: 9. This gives a total of 9 x 4 x 3 = 108 trials.
4. Counterbalancing: position of correct disk and distractor
5. Counterbalancing: distractor colors.

Visual Search Experiments

Experiment 1: Line Orientation

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 4, or 9 line segments.
4. If one of the line segments is vertical, S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 4, 9). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.
4. Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. For 9 item case: counterbalance nonant (a neologism, referring to any one of the 9 squares created by the 3 x 3 subdivision of the display) containing target, random placement of target in that nonant. Distractors placed at random in remaining quadrants/nonants.  The counterbalancing of target position in 9 item case is as follows. The target appears in each nonant once, and in three of the nonants twice.  Three versions of the experiment will be used which differ in the three nonants that are seen twice.  Each version of the experiment will be seen by one third of the subjects. In this way we counterbalance the 9 item case over subjects, whereas we counterbalance the 4 item case within subjects.

Experiment 2: Color

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 4, or 9 colored disks.
4. If one of the line segments is green, S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 4, 9). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.
4. Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. For 9 item case: counterbalance nonant containing target, random placement of target in that nonant. Distractors placed at random in remaining quadrants/nonants

Experiment 3: Convexity/concavity

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 4, or 9 shaded spheres.
4. If one of the spheres is concave, S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 4, 9). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.

Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. For 9 item case: counterbalance nonant containing target, random placement of target in that nonant. Distractors placed at random in remaining quadrants/nonants.

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 4, or 9 silhouettes, at most one of which is heart-shaped and the remainder are teardrop-shaped.
4. If one of the silhouettes is a heart, S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 4, 9). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.

Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. For 9 item case: counterbalance nonant containing target, random placement of target in that nonant. Distractors placed at random in remaining quadrants/nonants.

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 4, or 9 illusory lines, at most one of which is vertical and the remainder are horizontal.
4. If one of the illusory lines is vertical, S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 4, 9). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.

Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. For 9 item case: counterbalance nonant containing target, random placement of target in that nonant. Distractors placed at random in remaining quadrants/nonants.

Experiment 6: Subjective necker cubes

Each trial will go as follows:

1. S views blank screen, tells experimenter when they are ready to begin the trial, and experimenter then starts the trial.
2. A fixation cross appears at the center of the screen for 0.5 seconds; S fixates the cross.
3. The fixation cross disappears, and is replaced by a display containing 1, 2, or 4 sets of eight disks with white lines through each disk, at most one of which forms a subjective necker cube and the remainder do not. The distractors are made by randomly rotating, in place, each disk that forms a subjective necker cube, but keeping all disks in the same spatial relationships.
4. If one of the sets of disks forms a subjective necker cube S presses a "YES" button; otherwise S presses a "NO" button.

1. Independent variables: Target (present, absent) and number of items (1, 2, 4). These variables are fully crossed, in a 2 x 3 design.
2. Dependent variables: Percent correct answers; reaction times.
3. Repetitions of each condition: 12. This gives a total of 12 x 2 x 3 = 72 trials.

Counterbalancing: position of target on screen. For 1 item case: target placed at random (uniform distribution). For 2 item case: counterbalance upper versus lower hemifield, and left versus right hemifield; in half of these trials the one item is randomly placed in the left hemifield, the other in the right hemifield; in the other half of these trials the one item is randomly placed in the upper hemifield, the other in the lower hemifield. For 4 item case: counterbalance quadrant containing target, random placement of target in that quadrant. Distractors placed at random in remaining quadrants/nonants.

References

Think of this as a partial reading list!

[1] Tetewsky, S.J. & Duffy, C.J. 1999. Visual loss and getting lost in Alzheimer's disease. Neurology, 52, 958-965.  Abstract

[2] Hof, P.R. & Bouras, C. 1991. Object recognition deficit in Alzheimer's disease: possible disconnection of the occipito-temporal component of the visual system. Neuroscience Letters, 122, 53-56.

[3] Mendez, M.F., Mendez, M.A., Martin, R., Smyth, K.A., & Whitehouse, P.J. 1990. Complex visual disturbances in Alzheimer's disease. Neurology, 40, 439-443.  Abstract

[4] Armstrong, R.A. 1996. Visual field defects in Alzheimer's disease patients may reflect differential pathology in the primary visual cortex. Optometry and Vision Science, 73, 677-682.  Abstract

[5] Trick, G.L. & Silverman, S.E. 1991. Visual sensitivity to motion: Age-related changes and deficits in senile dementia of the Alzheimer type. Neurology, 41, 1437-1440.

[6] Cronin-Golomb, A., Corkin, S., Rizzo, J.F., Cohen, J., Growden, J.H., & Banks, K.S. 1991. Visual dysfunction in Alzheimer's Disease: Relation to normal aging. Annals of Neurology, 29, 41-52.

[7] Katz, B & Rimmer, S. 1989. Ophthalmologic manifestations of Alzheimer's Disease. Survey of Ophthalmology, 34, 31-43.

[8] Horwitz, B., McIntosh, A.R., Haxby, J.V., Furey, M., Salerno, J.A., Schapiro, M.B., Rapoport, S I., & Grady, C.L. 1995. Network analysis of PET-mapped visual pathways in Alzheimer type dementia. NeuroReport, 6, 2287-2292.

[9] Atchley, P. & Andersen, G.J. 1998. The effect of age, retinal eccentricity, and speed on the detection of optic flow  components. Psychology and Aging, 13, 297-308.

[10] Fisher, D.L. & Glaser, R.A. 1996. Molar and latent models of cognitive slowing: Implications for aging, dementia, depression, development, and intelligence. Psychonomic Bulletin & Review, 3, 458-480.

[11] Johnson, S.H. & Rybash, J.M. 1993. A cognitive neuroscience perspective on age-related slowing: Developmental changes in the functional architecture. In J. Cerella et al. (Eds), Adult information processing: Limits on loss. San Diego, Academic Press,  143-173.

[12] Maylor, E.A. & Rabbitt, P.M.A. 1994. Applying Brinley plots to individuals: Effects of aging on performance distributions in two speeded tasks. Psychology and Aging, 9, 224-230.

[13] Small, J.A., Kemper, S., & Lyons, K. 1997. Sentence comprehension in Alzheimer's Disease: Effects of grammatical complexity, speech rate, and repetition. Psychology and Aging, 12, 3-11.

[14] Kemper, S. & Kemtes, K. 1999. Aging and message production and comprehension. In N. Schwarz et al. (Eds), Cognition, aging, and self-reports. Psychology Press/Erlbaum (Uk) Taylor & Francis, Hove, England UK,
229-244.

[15] Hartley, A.A. 1992. Attention. In F.I.M. Craik & T.A. Salthouse (Eds), The handbook of aging and cognition. Erlbaum, Hillsdale, New Jersey, 3-41.

[16] Scialfa, C.T., Kline, D.W., & Lyman, B.J. 1987. Age differences in target identification as a function of retinal location and noise level: Examination of the useful field of view. Psychology and Aging, 2, 14-19.

[17] Kane, M.J., Hasher, L., Stoltzfus, E.R., Zacks, R.T., & Connelly, S.L. 1994. Inhibitory attentional mechanisms and aging. Psychology and Aging, 9, 103-112.

[18] Gurnsey, R., Humphrey, G.K., & Kapitan, P. 1992. Parallel discrimination of subjective contours defined by offset gratings. Perception & Psychophysics, 52, 263-276.
 

Visual Quick Tests

We will add more visual tests to those below, and then put them all into a single Superlab experiment so that it will be easy to record responses.

1. Neon worm

2. Subjective Necker cube

3. White's brightness illusion

4. Left-right surfaces

5. Dot on hill

6. Dots on bumps

7. Schroeder staircase

8. Part boundary popout

9. Illusory square with no contrast
 
 
 

Related Links
 

Scott Makeig:  Independent Components Analysis and Cognitive Neuroscience

Matlab ICA Toolbox