RESUMEN

After a stroke involving the left occipitotemporal cortex our patient shows a word-length effect and has problems to identify letters or numbers in strings of symbols. But he is normal in identifying isolated letters and in non-verbally categorizing even complex images such as faces or natural scenes. His cortical lesion is stretching from the visual word form area (VWFA) anteriorly causing additional problems to name visual stimuli and to match acoustic stimuli with images. We conclude that our patient suffers from pure alexia without deficits to identify even complex visual stimuli. Our results directly contradict several explanations for letter-by-letter reading.

Asunto(s)

Alexia Pura/diagnóstico , Alexia Pura/psicología , Isquemia Encefálica/complicaciones , Reconocimiento Visual de Modelos , Accidente Cerebrovascular/complicaciones , Alexia Pura/etiología , Isquemia Encefálica/patología , Humanos , Masculino , Persona de Mediana Edad , Lóbulo Occipital/patología , Accidente Cerebrovascular/patología , Lóbulo Temporal/patología

RESUMEN

Visual awareness is a specific form of consciousness. Binocular rivalry, the alternation of visual consciousness resulting when the two eyes view differing stimuli, allows one to experimentally investigate visual awareness. Observers usually indicate the gradual changes of conscious perception in binocular rivalry by a binary measure: pressing a button. However, in our experiments we used gradual measures such as pupil and joystick movements and found reactions to start around 590 ms before observers press a button, apparently accessing even pre-conscious processes. Our gradual measures permit monitoring the somewhat gradual built-up of decision processes. Therefore these decision processes should not be considered as abrupt events. This is best illustrated by the fact that the process to take a decision may start but then stop before an action has been taken - which we will call an abandoned decision process here. Changes in analog measures occurring before button presses by which observers have to communicate that a decision process has taken place do not prove that these decisions are taken by a force other than the observer - hence eliminating "free will" - but just that they are prepared "pre-thresholdly," before the observer considers the decision as taken.