Unconscious response priming by shape depends on geniculostriate visual projection

Authors

  • Mika Koivisto,

    1. Department of Psychology, University of Turku, Turku, Finland
    2. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland
    Search for more papers by this author
  • Linda Henriksson,

    1. Low Temperature Laboratory, Brain Research Unit, Aalto University School of Science, Finland
    2. Advanced Magnetic Imaging Centre, Aalto University School of Science, Finland
    Search for more papers by this author
  • Antti Revonsuo,

    1. Department of Psychology, University of Turku, Turku, Finland
    2. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland
    3. School of Humanities and Informatics, University of Skövde, Skövde, Sweden
    Search for more papers by this author
  • Henry Railo

    1. Department of Psychology, University of Turku, Turku, Finland
    2. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland
    Search for more papers by this author

Dr M. Koivisto, 2Centre for Cognitive Neuroscience, as above.
E-mail: mika.koivisto@utu.fi

Abstract

It has been suggested that unconscious visual processing of some stimulus features might occur without the contribution of early visual cortex (V1/V2). In the present study, the causal role of V1/V2 in unconscious processing of simple shapes in intact human brain was studied by applying transcranial magnetic stimulation (TMS) on early visual cortex or lateral occipital cortex (LO) while observers performed a metacontrast-masked response priming task with arrow figures as visual stimuli. Magnetic stimulation of V1/V2 impaired masked priming 30–90 ms after the onset of the prime. Stimulation of LO reduced the magnitude of masked priming at 90–120 ms, but this effect occurred only in the early parts of the priming experiment. A control task measuring the visibility of masked primes indicated that the orientation of masked primes could not be consciously discriminated and that TMS did not influence the conscious visibility of the primes indirectly by reducing the effectiveness of the mask in the critical time windows. We conclude that feedforward sweep of processing from V1/V2 (30–90 ms) to LO (90 ms and above) is necessary for unconscious priming of shape, whereas conscious perception requires also the contribution of recurrent (feedback) processing.

Ancillary