Bracha, V., Zhao, L., Wunderlich, D.A., Morrissy, S.J. and Bloedel, J.R. (1997) Patients with cerebellar lesions cannot acquire but are able to retain conditioned eyeblink reflexes. Brain, 120, 1401-1413.
The purpose of these experiments was to examine the role of the human cerebellum in the acquisition and retention of conditioned reflexes. Normal human subjects and patients with cerebellar lesions were tested for their capacity to acquire, retain and express conditioned eyeblink responses. In acquisition tests, subjects were trained in a delay classical conditioning paradigm using a tone conditioned stimulus and a midline forehead tap as an unconditioned stimulus. While normal subjects developed anticipatory eyeblinks to the tone in one session, patients with cerebellar lesions failed to acquire conditioned responses in four consecutive training sessions. The conditioning deficit was bilateral even in patients with a unilateral cerebellar pathology. The same groups of subjects were tested for the presence of eyeblinks to a visual threat. in these experiments, both normal subjects and patients with cerebellar lesions exhibited a high level of responding when they saw an object approaching their face. These eyeblinks to the visual threat are probably naturally acquired conditioned responses because they extinguish in normal subjects if they are not reinforced by the unconditioned cutaneous stimulus. in addition, the stimulus of seeing an approaching object blocks the acquisition of classically conditioned eyeblinks to a new conditioned stimulus in normal subjects. These data imply thar patients with cerebellar lesions who cannot acquire new classically conditioned responses are able to retain and express conditioned eyeblinks which were acquired before the onset of the pathology. Consequently cerebellum-dependent neural substrates which are involved in learning new conditioned reflexes do not seem to be required for the storage of naturally learned conditioned responses.
Ohman, A. and Soares, J.J.F. (1998) Emotional conditioning to masked stimuli: Expectancies for aversive outcomes following nonrecognized fear-relevant stimuli. Journal of Experimental Psychology-General, 127, 69-82.
The role of conscious awareness in human Pavlovian conditioning was examined in 2
experiments using masked fear-relevant (snakes and spiders; Experiments 1 and 2) and fear-
irrelevant (flowers and mushrooms; Experiment 1) pictures as conditioned stimuli, a mild
electric shock as the unconditioned stimulus, and skin conductance responses as the primary
dependent variable. The conditioned stimuli were presented briefly (30 ms) and were effectively
masked by an immediately following masking stimulus. Experiment 1 demonstrated
nonconscious conditioning to fear-relevant but not to fear-irrelevant stimuli. Even though the
participants could not recognize the stimuli in Experiment 2, they differentiated between
masked stimuli predicting and not predicting shocks in expectancy ratings. However,
expectancy ratings were not related to the conditioned autonomic response.
Even though the participants could not recognize the stimuli in Experiment 2, they differentiated between masked stimuli predicting and not predicting shocks in expectancy ratings. However, expectancy ratings were not related to the conditioned autonomic response.
Schugens, M.M. and Daum, I. (1999) Long-term retention of classical eyeblink conditioning in amnesia. Neuroreport, 10, 149-152.
THE retention of classical eyeblink conditioning was investigated in amnesic patients 10 days and 2 months after original learning. During reacquisition, the first CR occurred earlier and the CR frequencies during the first 10 trials were higher than in the baseline session. The overall CR rates increased significantly across sessions during both acquisition and extinction. The amnesics did not differ from matched controls on any of these effects, although they did not recall previous conditioning sessions and did not became fully aware of CS-US contingencies. The smaller number of electrodermal responses to the CS tone during extinction in the amnesics may relate to their lack of insight into the change in the reinforcement schedule. (C) 1999 Lippincott Williams & Wilkins.