Laterality-Specific Perceptual Learning on Gabor DetectionNestor Matthews & Jenna Kelly

Department of Psychology, Denison University, Granville OH 43023 USA

The Motivating SyllogismPremise 1 - Laterality affects attention.

Premise 2 - Attention affects perceptual learning.Prediction - Laterality affects perceptual learning.

Operational Definitions: Laterality is a variable that describes the spatial distribution of stimuli. Unilateral stimuli are restricted either entirely to the left hemifield, or entirely to the right hemifield. Bilateral stimuli are distributed across the left and right hemifields. Attention is the selection of a sensory event. Perceptual learning –in vision- is any practice-driven improvement in visual ability.

Several previous studies support the premise that laterality affects attention. Specifically, a bilateral attentional advantage has been reported on several attentional tasks. These include motion tracking (Alvarez & Cavanagh, 2005), letter identification (Awh & Pashler, 2000), letter-orientation discrimination in displays that exhibit crowding (Chakravarthi & Cavanagh, 2009), and detecting Gabor targets while ignoring Gabor distractors (Reardon, Kelly & Matthews, 2009).

The premise that attention affects perceptual learning is supported by studies showing practice-driven improvements for attended, but not unattended, features of a given training stimulus. Such attentionally specific perceptual learning has been reported for a variety of features: Luminance vs orientation (Shiu & Pashler,1992); local vs global orientation (Ahissar & Hochstein, 1994); direction of motion vs speed of motion (Saffell & Matthews, 2003).

Synthesizing those prior findings, here we tested the prediction that laterality affects perceptual learning –with attention as the mediating factor. A Gabor detection task was chosen due to its elementary, and presumably broad reaching, nature. Gabor distractors between the cued positions increased the attentional-selection demand. Importantly, our study differs from most perceptual learning studies, which typically evaluate transfer-of-learning to an untrained task (feature) or an untrained stimulus location. Here, both the task (Gabor detection) and the discriminative-stimulus locations (four peripheral quadrants) were identical in the training and transfer-test phases. Under these conditions, learning that is specific to the trained laterality would be surprising.

Discussion Introduction

References

Attentional Cue

m

Stimuli Noise Masks

1. Which Letter?

2. Target Present?Yes (y)

OrNo (n)

Response Prompts

MethodStimulus Sequence On Each Trial

Results

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Alvarez & Cavanagh (2005). Independent resources for attentional tracking in the left and right visual hemifields. Psychological Science 16(8), 637-643.

Awh & Pashler (2000). Evidence for split attentional foci. Journal of Experimental Psychology: Human Perception and Performance 26(2), 834-846.

Chakravarthi & Cavanagh (2009). Bilateral field advantage in visual crowding. Vision Research, 49(13), 1638-1646.

Reardon, Kelly & Matthews (2009). Bilateral Attentional Advantage on Elementary Visual Tasks. Vision Research, 49(7), 692-702.

Saffell & Matthews (2003). Task-specific perceptual learning on speed and direction discrimination. Vision Research, 43(12), 1365-1374.

Shiu & Pashler (1992). Improvement in line orientation discrimination is retinally local but dependent on cognitive set. Perception & Psychophysics, 52(5), 582-588.

Ahissar & Hochstein (1993). Attentional control of early perceptual learning. Proceedings of the National Academy of Sciences, 90(12), 5718-5722.

Bilateral: No Distractors Bilateral: Distractors Unilateral: No Distractors Unilateral: Distractors

Target/ Distracter Configurations

Experimental Details

Practice generated laterality-specific increases in hit rates. Notably, this learning specificity occurred only when targets had to be detected to the exclusion of distractors –a hall mark of attentional selection.

The laterality-specific increases in hit rates cannot be explained by an increased liberal response bias, i.e., an enhanced tendency to report ,“yes, I see it”. This is because an increased liberal response bias would also generate higher false alarm rates. To the contrary, false alarm rates declined significantly after training.

The false alarm data also rule out the possibility that participants learned only to ignore the distractor positions that were presented during the training phase. If that were the case, then the false alarm reductions observed in the post-test would have been specific to the trained laterality. Instead, the post-test results show that false alarms declined equally at the trained and untrained lateralities.

In conclusion, the data confirm laterality-specific perceptual learning, mediated by attentional selection, i.e., detecting Gabor targets to the exclusion of spatially intervening Gabor distractors. The observed learning specificity is particularly surprising given the task and location constancy across training and transfer-test phases.

•Participants: 20 Denison University undergraduates•IVs: 2 (Session) x 2 (Laterality) x 2 (Distractor) x 2 (Group)

•Session = Pre vs Post: Laterality = Uni- vs Bilateral •Distractor = Absent vs Present: Group= Uni- vs Bilateral

•DVs:•Hits: “Yes” response when Gabor target present•False Alarms: “Yes” response when Gabor target absent

http://www.denison.edu/~matthewsn/plvss2010.html

Poster # 26.422Abstract # 1390

Session x Laterality x Group: F(1,18)= 8.833, p=0.008, partial eta^2=0.329

Four-Way Interaction Effect F(1,18)= P-value Partial Eta^2 PowerSession by Laterality by Distractor by Training

Group 9.429 0.007 0.344 0.827

Session x Laterality x Group: F(1,18)= 0.006, p=0.939, partial eta^2<0.001

Four-Way Interaction Effect F(1,18)= P-value Partial Eta^2 PowerSession by Laterality by Distractor by Training Group 0.063 0.805 0.003 0.056

D.V. = Hits D.V. = False AlarmsBilateral Stimuli Unilateral Stimuli

•Range-finding day identified individual stimulus durations•Pre-test with participant-specific parameters

(comprised all four conditions shown above)•5 training days; 10 trained bilaterally, 10 unilaterally•Post-test identical to pre-test•Laterality-specific learning indexed by 3-way interaction

(Session by Laterality by Group)

Training Paradigm

Session x Laterality x Group: F(1,18)= 0.002, p=0.963, partial eta^2<0.001 Session x Laterality x Group: F(1,18)= 0.257, p=0.619, partial eta^2=0.014