kelly shen and martin par é

“Nothing average ever stood as a monument to progress. When progress is looking for a partner it doesn't turn to those who believe they are only average. It turns instead to those who are forever searching and striving to become the best they possibly can. If we seek the average level we cannot hope to achieve a high level of success. Our only hope is to avoid being a failure.”

- A. Lou Vickery

Guidance of Eye Movements During Visual Conjugation Search: Local and Global Contextual Effects on Target Discrimination

Kelly ShenandMartin Paré

Presented by:Jason Chanfor joeLAB

July 15,2008

Introduction

• Attentional resources required for analysis of visual images

• Focal attention not important for feature search tasks, is important for conjunction search tasks

• Previous studies did not measure spatial allocation of attention; detailed information can be derived from eye movements

Key Questions

1. Are visual search strategies influenced by composition of stimuli?

2. Are visual search strategies influenced by arrangement of stimuli?

3. Is the timing of an initial saccade influenced by target discriminability?

Methods

• 3 female rhesus monkeys• Magnetic search coils or infrared camera• Primate chair

8-stimulus display

Adjacent distractor randomized

12-stimulus display

Colour-similar to colour-different distractor ratio randomized

0:11 ratio

Feature search based on colour

12-stimulus display

Colour-similar to colour-different distractor ratio randomized

8:3 ratio

12-stimulus display

Colour-similar to colour-different distractor ratio randomized

11:0 ratio

Feature search based on form

Results – Conjunction characteristics

• Conjunction less efficient than single feature• Longer search time for conjunction due to

increased # of saccades, not delayed response• Conjunction task only involved attentional

resources for saccade production

Results – Local contextual effects

Results – Local contextual effects

# of colour changes in display had no effect on accuracy or search time

Target colour = attentional bias

Results – Global contextual effects

Discussion – Display composition

• Flanking task effect: less visual processing necessary to identify stimulus

• Masking effect: deter identification of target

• CTVA (CODE theory + visual attention) account for local contextual effect

Discussion – Visual guidance

• Colour guiding feature for target search, esp. when proportion of same-colour stimuli low

• Search strategy = target-feature + salience

• Strategy not guided by only bottom-up

• Colour more discriminable than form

Discussion – Initial responses

• Initial responses from automatic process

• When & where based on limited visual information processing from display

• Visual processing limited: attentive scanning has limited opportunity to occur

1. Search strategies influenced by composition of stimuli?

• YES

2. Search strategies influenced by arrangement?• YES

3. Timing of an initial saccade influenced by target discriminability?

• NO

Conclusion

THE

END

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McCOLLOUGH EFFECT

the