(Esta questão foi respondida há dez meses em um comentário por Covertwalrus, que aparentemente não pretende postar uma resposta, então eu farei.)
A história é de fato "A realidade de Susie" por Bob Stickgold também conhecido como Robert Stickgold, PhD , publicado originalmente em Mundos de If , Maio-junho de 1973 , disponível no Arquivo da Internet . A história é exatamente como você descreveu:
Chuck was waiting when they reached the lab and he was eager to get started. Steve gave Susie her nut and chatted inanely with her for a couple of minutes. Then he gave Susie the watch to play with. As always, Susie accepted it readily. She danced around the cage, pausing now and then to listen to its ticking. After a few minutes Steve wrestled it away from her and slipped it under the bowl. This time it would stay there. In more than a thousand trials during the past year Susie had always seen it disappear and reappear behind Mama. This time it would not.
As always, Susie ran to the surrogate Mama and reached for the watch. It wasn’t there. Susie froze. She sat motionless for exactly thirty seconds and then started screaming wildly. Steve showed Susie the watch under the bowl and then covered it again. She stared at the bowl for long seconds and then slowly lifted her hands to cover her eyes.
“She’s trying to' make it disappear,” whispered Sue. “She wants it to disappear. Oh, God — she will go mad this time.”
Susie uncovered her eyes, walked cautiously to Mama, and peered behind the dummy parent. Immediately she started chattering happily. She reached behind Mama. In an instant she had the watch in her hand.
For a long time Steve, Sue and Chuck simply stared at Susie and the watch. No one said a word. No one moved. What was there to say? Without breaking the silence Steve examined the cage. The trapdoors were all wired properly. The releases were in position. The loading platforms were all empty and the receptacle beneath the bowl was empty. He opened the door to the cage and lifted the bowl. There was nothing there. Three blank faces stared at the bowl.
Steve turned to the others. “Have I gone crazy? Did either of you see it? It disappeared. Didn’t it?” His voice verged on hysteria.