Predefined stimuli

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MonkeyCantab is supplied with a set of built-in stimulus sets. They are:

 

Stimulus name

where X is from 1 to...
•University of Cambridge ID/ED stimuli: shape set, line set.

univcam_IDED_shape_X

univcam_IDED_line_X

54

44

camcog_mdms0_X

camcog_mdms5_X

camcog_mdms6_X

camcog_mdms7_X

430

469

16

10

camcog_pal0_X

camcog_pal1_X

camcog_pal2_X

camcog_pal3_X

camcog_pal4_X

camcog_pal5_X

67

17

17

17

17

18

camcog_star0_X

camcog_star1_X

camcog_star2_X

camcog_star3_X

camcog_star4_X

48

48

48

48

48
•Cambridge Cognition ID/ED stimuli: sets 0 to 8, both of which have a shape subset and a line subset.

camcog_nedi0shape_X

camcog_nedi0line_X

camcog_nedi1shape_X

camcog_nedi1line_X

camcog_nedi2shape_X

camcog_nedi2line_X

camcog_nedi3shape_X

camcog_nedi3line_X

camcog_nedi4shape_X

camcog_nedi4line_X

camcog_nedi5shape_X

camcog_nedi5line_X

camcog_nedi6shape_X

camcog_nedi6line_X

camcog_nedi7shape_X

camcog_nedi7line_X

camcog_nedi8shape_X

camcog_nedi8line_X

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

3

2

 

These stimulus sets can be used in a number of ways.

•You can make your own copy of them by importing them into your configuration file (giving them a name of your choice), and then edit them for your own needs. See The Visual Object Library.
•You can refer to them directly, whereever you are asked to supply a stimulus name, using the names shown above. For example, the first stimulus in the University of Cambridge ID/ED shape set is called univcam_IDED_shape_1. (Please note that if you create your own stimulus with the same name as a predefined stimulus, MonkeyCantab will choose your version.)
•You can use whole sets of stimuli in tasks that require large numbers of stimuli, such as the D(N)MTS and PAL tasks. These tasks can manipulate the stimuli, to generate a much larger set of potential stimuli (for example, by altering the colours of each quadrant).

 

Technical details of the stimulus-generating techniques used

 

•The PAL task varies the stimuli by altering the colour of each quadrant; since there are 4 quadrants per stimulus and 7 possible colours (red, green, yellow, blue, magenta, cyan, white), there are 7^4 = 2401 variants on each stimulus (giving, for the PAL0 stimulus set, 160,867 possible stimuli in total). You can refer to them directly; for example, variant 817 of stimulus 65 of the PAL 0 set is called camcog_pal0_65_PV817. Variants are numbered from 0.

 

•The DNMTS task varies stimuli in several ways; a single varant number is interpreted according to the variation system required. Stimuli are created in groups of four (even if not all four are to be used on a given trial) using the specified stimulus, plus the three that follow it in the set (wrapping round to the start if need be).
•(1) If shape quadrants are to be shuffled, then the quadrants are exchanged between stimuli, keeping them in the same place (e.g. top right), in a manner that gives 64 ways of generating 4 stimuli from the 4 stimuli that we started with.
•(2) Colour reassignment is applied. This can be:
•unmodified (UN) (don't change a thing). If shapes are also not shuffled, this is intended to correspond to the old DOS Monkey CANTAB scheme of "STIMULUS DIRECT".
•vary colours (VC) (alters the colours of each quadrant of each of the 4 stimuli in the same way; as there are 7 usable colours, this gives 7*7*7*7 = 2401 further variations).
•monochrome, shape-only discrimination (MS) (all stimuli are made the same colour; there are 7 possible colours) [remember, monochrome means one colour, not black-and-white]. The colour is that of the top-left quadrant of the first shape in the group (shifted by the value of the variant). This is intended to correspond to the old DOS Monkey CANTAB scheme of "MONOCHROME / SHAPE".
•monochrome, shape-only discrimination, fixed colour (MF) (all stimuli are made the same colour; the user specifies this colour) [remember, monochrome means one colour, not black-and-white]. This option is new as of Jan 2007. The colours are as follows (with red/green/blue components shown on a scale of 0-255):

 

•colour 0 = black (R 0, G 0, B 0)
•colour 1 = red (R 255, G 0, B 0)
•colour 2 = green (R 0, G 255, B 0)
•colour 3 = yellow (R 255, G 255, B 0)
•colour 4 = blue (R 0, G 0, B 255)
•colour 5 = magenta (R 255, G 0, B 255)
•colour 6 = cyan (R 0, G 255, B 255)
•colour 7 = white (R 255, G 255, B 255)
•colour 8 = orange (R 255, G 165, B 0)
•colour 9 = indigo (R 75, G 0, B 130)
•colour 10 = violet (R 238, G 130, B 238)
•colour 11 = moccasin (R 255, G 228, B 181)
•colour 12 = light slate grey (R 119, G 136, B 153)
•colour 13 = saddle brown (R 139, G 69, B 19)

 

There is only one colour variant, because only one colour can be used at one time (but the user can specify which colour this is).

 

•monochrome, colour-only discrimination (MC) (all stimuli are made the same shape; all stimuli are monochrome [meaning one colour, not black-and-white] but the colour of each stimulus in the set of four is different; there is only 1 possible variation with this theme before colours are repeated, which can't be done as it would make at least one stimulus non-unique in the full set). This is intended to correspond to the old DOS Monkey CANTAB scheme of "MONOCHROME / COLOUR".
•monochrome, mixed (MM) (one distractor has a different shape and a different colour to the target; one has the same shape but a different colour; one has the same colour but a different shape. There are seven available colours, so 3 variations of two colours each). This is intended to correspond to the old DOS Monkey CANTAB scheme of "MONOCHROME / MIXED".
•seven colours per trial (SC) (the target uses four colours; the incorrect stimulus uses the three remaining unused colours and one colour that overlaps with the target stimulus, though the overlapping colour is never in the same quadrant in the incorrect stimulus as it is in the target). The target stimulus can have up to 7*6*5*4 = 840 colour variations, so that limits the number of trial-unique stimuli; the further variations in the distractor (namely 4 possible choices of overlapping colour, 3 possible choices of quadrant to place that overlapping colour, and 3*2*1 possible arrangements of the unique colours in the distractor) do not contribute to trial uniqueness and are chosen in a way that is deterministic but tends to vary from trial to trial (specifically, the variant number is re-used to determine these, so these parameters covary with the colour scheme of the target; this is not obvious to the user!). 18-Oct-2004: this scheme, when used with one target and only the first incorrect stimulus, is intended to correspond to the old DOS Monkey CANTAB scheme of "PAIRED STIMULI", as used by Weed et al. (1999) Cognitive Brain Research 8: 185. With the MDMS5 stimulus set (469 stimuli), this gives 840*469/2 = 196,980 unique trials with two stimuli per trial. It can also be used with four stimuli per trial; a second pair of stimuli, related in the same way as the target/first incorrect stimulus, are added to the set. These extra stimuli will not necessarily share exactly one colour with the target. Please note that this scheme does not work well with 3 stimuli per trial (one target plus two incorrect stimuli), as the target is picked at random from the first three stimuli - so there is no guarantee that it will share exactly one colour with the incorrect stimuli.
•Therefore, since DMTS stimulus set 0 has 430 stimuli in it, the most variable stimulus set you can generate (using quadrant shuffling plus full colour variation) is 430 x 64 x 2401 = 66,075,520 stimuli. If four stimuli are used on each trial, this gives you 16,518,880 possible unique trials. I feel that should be enough.
•DMTS-shuffled stimuli can be referred to by appending _DM, then _SS for shape quadrant shuffling or _NS for no shuffling, then _UN, _VC, _MS, _MC, _MM, or _SC for one of the colour variation schemes, and then a variation number, then "_", and then which of the four generated stimuli you want. So the fourth stimulus within the set generated by the last unique shape-shuffled, colour-varying variation on stimulus 200 of DMTS set 0 might be camcog_mdms0_200_DM_SS_VC153663_3. An exception: the _MF scheme takes an additional parameter: the number immediately after "MF" is the colour, and then an underscore follows, and then the variant number and so on (e.g. camcog_mdms0_200_DM_SS_MF7_0_3, where 7 is the colour and 0 is the variant). Please note that as the stimuli are generated in sets of 4, you may end up with non-unique stimuli if you generate further sets that overlap. For example, if you generate a set of 4 stimuli based on stimulus 1 (which involves looking at stimuli 2, 3, and 4), and you show all the stimuli to the subject, then to guarantee unique stimuli you should request the next four starting with stimulus 5, not stimulus 2. Variants, and stimuli within a set of four, are numbered from 0.

 

Stimulus provenance and copyright

 

•The University of Cambridge ID/ED stimuli were developed by A.C. Roberts and colleagues at the University of Cambridge (e.g. Dias R, Robbins TW, Roberts AC, 1996, Nature 380: 69; Dias R, Robbins TW, Roberts AC, 1997, J. Neurosci. 17: 9285). The versions presented here are the stimuli in use at the University of Cambridge in 2003. To the extent that these stimuli are copyrightable (one, for example, is a single horizontal line, which probably cannot be the subject of copyright), copyright to some of these stimuli may have been transferred from the creators to Cambridge Cognition Ltd (see below). However, shapes 22, 51, 52, 53, and 54, and lines 1, 22, 28, 41, 42, 43, and 44 are not part of Cambridge Cognition's stimulus set, and copyright to these stimuli probably lies with the creators.
•The Cambridge Cognition ID/ED stimuli are a subset of the University of Cambridge ID/ED stimuli. Cambridge Cognition used these stimuli under licence from A.C. Roberts, T.W. Robbins, and colleagues, and probably held the copyright to these stimuli.
•Copyright to the Cambridge Cognition PAL, D(N)MTS, and STAR stimuli was held by Cambridge Cognition (to the extent that such stimuli are copyrightable, as always).
•From July 2004, copyright to those stimuli owned by Cambridge Cognition Ltd was transferred to Campden Instruments Ltd (the US parent company of which is the Lafayette Instrument Company).