Systems neuroscienceEffects of perceptual learning in visual backward masking on the responses of macaque inferior temporal neurons
Section snippets
Subjects
Four juvenile male monkeys (Macaca mulatta) were used. All procedures were approved by the K. U. Leuven Ethical Committee for animal experiments and followed U.S. National Institutes of Health guidelines. All efforts were made to minimize the number of animals used and their suffering. Separate surgeries were performed in order to implant a plastic head restraint, a scleral search coil, and a plastic recording chamber (Crist Instruments, Hagerstown, MD, USA). Monkeys were anesthetized with
The neural correlates of object-specific learning
The initial aim of our experiments was to investigate the neural correlates of object-specific training effects. Two monkeys (1A and 1B) were trained with a particular set of stimuli, and we compared behavioral performance and neuronal responses after training for this trained set of stimuli and untrained sets of stimuli.
The monkeys performed a masked same/different task in which they compared two objects of which the first was masked (Fig. 1). The effect of SOA was measured for two groups of
Discussion
We found that training in recognizing masked objects improved monkeys’ recognition performance. A substantial part of this training effect transferred to untrained objects. The small object-specific component of training-related improvements, found in only one monkey, was associated with a transient, object-specific increase in neuronal selectivity. A comparison of trained and untrained monkeys suggested that the strong object-independent behavioral effects were associated with a reduction of
Conclusion
In conclusion, our results suggest that training in backward masking is associated with a marked decrease in mask responses, in addition to a transient object-specific increase in object selectivity at short SOA in one monkey. These new results reveal how the visual system deals with the specific constraints of a perceptual learning paradigm, such as backward masking, in order to enhance the processing of degraded but relevant objects and to suppress the processing of salient but irrelevant
Acknowledgment
We thank M. De Paep, P. Kayenbergh, G. Meulemans, and G. Vanparrys for technical assistance, and C. Baker and D. Cox for their helpful comments on a previous version of the manuscript. This work was funded by GSKE and IUAP 5/10 (R.V.), IDO/02/004 (R.V. and J.W.), Human Frontier Science Program (RGP 18/2004 (R.V.)). H.O. was supported by the Human Frontier Science Program and the Fund for Scientific Research Flanders.
References (37)
- et al.
Learning pop-out detection: Specificities to stimulus characteristics, II: Retinotopic organization
Vision Res
(1996) - et al.
The time course of visual processing: Backward masking and natural scene categorisation
Vision Res
(2005) - et al.
Perceptual learning in object recognition: Object specificity and size invariance
Vision Res
(2000) - et al.
The neural basis of perceptual learning
Neuron
(2001) - et al.
Effects of visual experience on the representation of objects in the prefrontal cortex
Neuron
(2000) Stimulus specific adaptation in inferior temporal and medial temporal cortex of the monkey
Behav Brain Res
(1996)- et al.
Impact of learning on representation of parts and wholes in monkey inferotemporal cortex
Nat Neurosci
(2002) Neural mechanisms for visual memory and their role in attention
Proc Natl Acad Sci U S A
(1996)- et al.
Competition for consciousness among visual events: the psychophysics of reentrant visual processes
J Exp Psychol Gen
(2000) - et al.
What’s new in visual masking?
Trends Cogn Sci
(2002)