Investigating reinforcer magnitude and reinforcer delay: a contingency management analog study
Experimental and Clinical Psychopharmacology (2012) - Comment
pubmed: 22686494  doi: 10.1037/a0027802  issn: 1936-2293  issn: 1064-1297 

Robert R. Packer, Donelle N. Howell, Sterling McPherson, John M. Roll