Experiment 1: Cross-situational word mapping, retention, and generalisation in typical development and autism
Materials
	Stimuli included six novel words selected from the NOUN database (Horst & Hout, 2016) and colour photographs of twelve unfamiliar objects. The novel words (Virdex, Nelby, Gasser, Blicket, Fiffin, Teebu) were recorded by a female speaker. The pictures of unfamiliar objects were divided into 6 sets. Each set included a ‘named object’ (which was paired with a novel word during training) and a ‘shape match’ (a differently-coloured variant of the named object that was presented in generalisation test trials). Each shape match was the same colour as a named object from a different set, and therefore served as a colour match in generalisation test trials. The relationship between shape and colour of object stimuli within and across sets is illustrated in Figure 1.  Colour photographs of 12 familiar objects (cat, shoe, bed, tree, cow, banana, duck, dog, apple, flower, car, ball) were used in warm-up trials. Familiar objects were selected on the basis that most children understand their linguistic labels by 15-months (Fensen et al., 1994). All stimuli were presented via a Microsoft Surface Pro 4 tablet computer. Pictures of objects were approximately 4cm x 4cm in size, and separated on screen by 10cm. 

Named Object

Shape Match

Colour Match

Set 1

Set 2

Set 3

Set 4

Set 5

Set 6

Fig. 1 Sets of unfamiliar objects used in Experiments 1 and 2

	Procedure
	Participants were tested individually in their own schools and were accompanied by a familiar adult when required. Children completed two test sessions on different days. Children were administered the BPVS, Leiter-3, and the Mullen Scales language modules over a series of sessions before completing the word learning task after a 1-week break. The word learning task consisted of the following stages delivered in a fixed order: 1. Warm-Up trials, 2. Learning trials, 3. Delay, 4. Retention and Generalisation trials. The word learning task was delivered on the tablet computer, which was placed in front of the child on a table. The experimenter sat quietly while the participant was engaged in the task and offered verbal praise for attention and good behaviour. The experimenter did not provide corrective feedback at any stage. 
	Warm-Up trials. To familiarise children with the format of the task and its response method, children completed 4 warm-up trials. Children were presented with two pictures of familiar objects on the left and right of the tablet’s screen, and heard a female voice (presented through the tablet’s speakers) say “Look!” in an excited tone. After viewing the pictures for 3 seconds, the same voice asked them to identify one of the objects (“Which is the cat? Touch the cat”). Following a correct response, the experimenter issued praise and reinforced the identity of the object (e.g. “Great job, that is the cat!”). Following an incorrect response, the experimenter provided corrective feedback (e.g. “Actually, this is the cat. Can you touch the cat? Well done, you touched the cat!”). The requested object was positioned to the left on two trials, and the right on two trials. Trial order was randomised for each participant.
	Learning trials. This stage provided a context in which children could actively learn six novel word-object pairings. Children completed 48 training trials, administered in two blocks of 24 trials (order counterbalanced across participants). The length of this training stage was based on Smith and Yu’s (2008) successful use of 30 trials with TD 12-month-olds. To minimise the likelihood of fatigue, children received a 30-second break after completing the first block of training trials.
	On each training trial, children were presented with photographs of two unfamiliar objects positioned to the left and right of the tablet’s screen accompanied by a female voice directing them to “Look!” (see Figure 2). After viewing the pictures for 3 seconds, the same voice asked them to identify one of the objects (e.g. “Which is the blicket? Touch the blicket”). Following the child’s response, the pictures disappeared and the next trial was presented. Individually, these trials are ambiguous (e.g. either object could be the word’s referent), but cross-situational statistics enabled children to disambiguate the correct word-referent pairings. For example, on the first trial the child might hear the word “blicket” while viewing an X and a Y. At this point, either X or Y could be the target referent. Then, on a subsequent trial, the child experiences “blicket” paired with a Z and an X. If the child is sensitive to cross-trial co-occurrence frequencies, they should correctly map “blicket” onto the X – the object it is experienced with consistently. 

“Look!”

Initial presentation
(3s)

Referent request

“Which is the blicket? Touch the blicket.”

Fig. 2 Example training trial in Experiment 1

	Words occurred an equal number of times in each block and word-object pairings were randomised for each participant. In each block, every object occurred as a target four times and as a foil four times (thus, each target word-object pairing was experienced eight times in total). The target object appeared equally often on the left and right of the screen. The order of trials within blocks was randomised. Children’s active learning was tracked by recording the accuracy of their selections. If a child refused to respond on a particular trial, the experimenter progressed to the next trial by pressing a discrete asterisk button in the upper right-hand corner of the screen. This enabled children to proceed with the task without the experimenter needing to select a referent object on their behalf.
Delay. After completing the last training trial, the child played with the experimenter for 5 minutes. The tablet was not used during this period. 
Retention and generalisation test trials. To re-engage children’s attention to the task, three new warm-up trials with pictures of familiar objects were administered. Here children were presented with three objects per trial positioned to the left, middle, and right of the screen. The requested object appeared in each of the three possible locations on one trial, and trial order was randomised. Thus, children were familiarised with the new “middle” location and had selected targets in each location before the test trials.
	Children then completed 12 retention trials and 12 generalisation trials (see Figure 3). Each word was tested on two retention trials and two generalisation trials. For retention trials, three of the named objects were presented on the tablet’s screen (positioned at the left, middle, right of the screen). After viewing the pictures for 3 seconds, children heard a female voice asking them to identify one of the objects (e.g. “Which is the blicket? Touch the blicket”). The purpose of these trials was to assess children’s memory of the exact word-referent pairings that were experienced during the training trials. For generalisation trials, children were presented with differently-coloured variants of named objects (i.e. shape/colour matches). After viewing the pictures for 3 seconds, children heard a female voice asking them to identify one of the objects (e.g. “Which is the blicket? Touch the blicket”). Crucially, one object was the same shape as the label’s original referent, but different in colour (shape match), while another object matched the original referent on colour, but not shape (colour match). The third object, a shape match, for a different named object served as a distracter. The purpose of these trials was to assess whether children’s extension of labels to novel referents is systematically influenced by shape or colour.
Importantly, all choice objects in retention and generalisation trials were of equal familiarity. Each object was used as a foil in two retention trials and two generalisation trials. To provide the necessary level of control when presenting stimuli, object groupings were fixed. The order of trials within blocks was pseudo-randomised such that the same word was not tested on consecutive trials (e.g. “blicket” Retention trial followed by “blicket” Generalisation trial), and no more than two trials of the same type occurred in a row. The target object appeared equally often on the left and right of the screen, and never occurred in the same location on more than 2 consecutive trials. Pictures of objects were exactly the same size as those presented during the training trials. The accuracy of children’s selections were recorded.  

(b)

(b)

(a)

“Blicket”

Generalisation test trial

Retention test trial

(c)

(d)

(e)

Fig. 3 Example retention and generalisation test trials in Experiments 1 and 2; (a) named target object, (b) non-target named objects, (c) shape match for named target object, (d) colour match for named target object, (e) shape/colour match for non-named object

Experiment 2: The effects of attentional cues on cross-situational word mapping, retention, and generalisation in typical development and autism
Materials
Stimuli were exactly the same novel words and colour photographs of objects (familiar and unfamiliar) as used in Experiment 3. Two short videos were created depicting a female face looking forward before turning to look left or right.  All stimuli were presented via a Microsoft Surface Pro 4 tablet computer. 
Procedure
The paradigm was exactly as described for Experiment 1 with some adjustments to the warm-up trials and training trials due to introducing social or non-social cues. All other stages, and the order of administration, remained the same. 
Social cue condition. Children completed 4 warm-up trials followed by 48 training trials, administered in two blocks of 24 trials. The stimuli and format were as previously described, with one exception: a female face appeared in between each pair of objects. On appearance, the face was looking directly forwards, and children heard a female voice directing them to “Look!”. After 3 seconds, the face turned to one of the objects (the target named object) and the same voice asked them to identify one of the objects (e.g. “Which is the blicket? Touch the blicket”; see Figure 4). Following the child’s response, the pictures disappeared and the next trial was presented. Thus, the face’s direction of gaze and corresponding head turn provided cues to the referent of each word, effectively reducing the ambiguity of each individual training trial (see Wu, Gopnik, Richardson & Kirkham, 2010). 
Non-social cue condition. As above, children completed 4 warm-up trials followed by 48 training trials (administered in two blocks). On each trial, children were presented with photographs of two objects positioned to the left and right of the tablet’s screen accompanied by a female voice saying “Look!”. A star shape also appeared between the two objects. We reasoned that children in the social cue condition would look at the face before the head turn, dividing their attention between the three elements on screen. The star appeared in the initial portion of training trials in the non-social condition to divide children’s attention in a similar way before experiencing the directional cue. After viewing the pictures for 3 seconds, the star disappeared, and one of the objects (the target named object) was “highlighted” by a green border and the same voice asked them to identify one of the objects (e.g. “Which is the blicket? Touch the blicket”; see Figure 4). Following the child’s response, the pictures disappeared and the next trial was presented. Here, the green border provided a non-social attentional cue to the referent of each novel word.

“Look!”

Social Cue Condition

Initial presentation
(3s)

Referent request

“Which is the blicket? Touch the blicket.”

Non-social Cue Condition

“Look!”

Initial presentation
(3s)

Referent request

“Which is the blicket? Touch the blicket.”

Fig. 4 Example training trials in the social and non-social cue conditions of Experiment 2