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Visual Search Deficits in Williams Buren Syndrome. Montfoort, I., Frens, M.A., Lagers-Van Haselen, G.C., & van der Geest, J.N. Williams Syndrome. Genetic disorder Characteristics of WS Impaired global visual processing (Bihrle, Bellugi, Delis & Marks, 1989)

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visual search deficits in williams buren syndrome

Visual Search Deficits in Williams Buren Syndrome

Montfoort, I., Frens, M.A., Lagers-Van Haselen, G.C., & van der Geest, J.N.

williams syndrome
Williams Syndrome
  • Genetic disorder

Characteristics of WS

  • Impaired global visual processing (Bihrle, Bellugi, Delis & Marks, 1989)
  • Deficits in visuospatial memory (Vicari, Bellucci & Carlesimo, 2005)
  • Motor problems (Van der Geest, et al., 2005, Withers, 1996)
visual search
Visual Search

What is visual search?

  • Attempt to find a ‘target’ in the visual scene

e.g. Where is the orange square?

Serial search is likely to use visuospatial memory and working memory

visual search and eye movements
Visual search and eye movements

Definition of serial search

  • “Using saccadic eye movements to look for an item of interest. Searching for one item after another until the target is found.”

Visual Search and eye movements

  • Saccadic eye movements allow the observer to look for interesting items in the display
  • Foveal fixation = information gathering
  • Scan path = the path used to search for items
  • Impairments in visual processing and working memory will lead to less efficient visual search in Williams participants than in normal controls


IQ = 66-85

Measured visual acuity (Landolt-C test), no significant

differences were found in the visual acuity of the three

groups (p=0.2)

  • Subjects had a chin rest to restrain head movements
  • Monocular vision with dominant eye
  • Calibrated eye movements
  • Eye-Link 2.04
    • Records monocular gaze positions using infrared video-oculography
  • 4-11 white items (squares, circles, triangles)
    • Target white with a black dot
    • Black dot very small so had to foveate on the target
    • 10 search displays
    • Same order for each participant
  • Red pop-out stimulus
    • To attract attention
    • To avoid participants looking straight at the target
example trial
Example Trial

Pop-out Distracter


Start Point, visible before start of trial




  • Eye movements classed as saccades if over 30º/s


  • >80m/s (to exclude fixations prior to correction saccades)
  • Target fixation if within 3º of target
  • If more than one item within 3º, closest item was classed as the item fixated on
  • Search time
  • Fixation duration
  • Number of fixations
  • Type of fixations (mis- and re-fixations)
  • Don’t analyse the QL group
  • Analysed young (<18 years) WS cf. to older (>18 years) WS, no differences, so collapsed across the group
search efficiency
Search Efficiency

Location of Target

  • WS found target within 5 seconds on 67% of trials, control 99%
  • WS were slower than control

Median search time

  • WS 3.6 (+/- 0.3sec)
  • TD 1.7 (+/- 0.1 sec)

Increase in the number of display elements led to

increase in RT

  • WS 334 m/s per element
  • Control 157 m/s per element
fixation duration
Fixation Duration

Fixation Duration

  • 37m/s longer in WS

First fixation

  • Longer than subsequent fixations
  • WS 363 (+/-6) m/s
  • Control 337 (+/-5) m/s
  • Marginal difference between groups, p=.06

First Saccade

  • 58% trials (both groups) directed at the red dot
number of fixations
Number of Fixations

Locate target

  • WS group needed an average of 2.2 more fixations than the control group to find the target
  • Had more refixations and misfixations than control group

Increase in the number of items in the display

  • WS = 1.4 fixations/element
  • Control = 0.7 fixations/element

Random search?

  • WS were more similar to a search that had no memory
  • Even after removal of fixations, search was more similar to a search without memory
refixations and misfixations
Refixations and Misfixations

WS Group

  • The number of misfixations increased for trials containing more items
  • 1 in 8 refixations
  • 1 in 4 misfixations

Control Group

  • Few misfixations in the control group


  • Subtract total number of refixations and misfixations from total fixations then WS group do not need more fixations than control to complete the task

Could this be due ocular motor problems?

  • Some degree of saccadic dysmetria is found in WS, including a higher number of correction saccades (e.g. Van der Geest et al., 2004)
  • However…
    • Inaccuracy in eye movements for the WS group were roughly 2.5º whilst misfixations were 3º
    • This does not explain the unsystematic search pattern in the WS group

Could this be due to impaired visuospatial processing?

  • The WS group had longer fixations, so perhaps this is linked to local or global processing, but the current study does not separate the effect of the two processes

Could it be memory?

  • Hooge et al. (1999) propose the first fixation can be used to plan search path
  • WS and TD group had longer first fixations
  • First fixation longer than the mean duration of subsequent fixations for both groups
search and memory
Search and Memory

Could it be memory…?

  • The difference in the first fixation to subsequent fixations was smaller in the WS group than the control group, so perhaps a problem with memory for the WS group?
  • WS group: Search was poorer than the predicted random pattern of search (which proposes each fixation is at a separate point and there are no misfixations)
  • For the WS group, this suggests there may be a problem in memory for locations
could it be iq
Could it be IQ?
  • Possibly not, as low-IQ individuals looked similar to normal controls
    • But, results of the low IQ group are not explicitly discussed in the article